[1Co 10:5 ASV] (5) Howbeit with most of them God was not well pleased: for they were overthrown in the wilderness.
[Num 14:16 KJV] (16) Because the LORD was not able to bring this people into the land which he sware unto them, therefore he hath slain them in the wilderness.
[Brenton LXX Num 14:16] (16) Because the Lord could not bring this people into the land which he sware to them, he has overthrown them in the wilderness.
[Swete LXX] 16 Παρὰ τὸ μὴ δύνασθαι Κύριον εἰσαγαγεῖν τὸν λαὸν τοῦτον εἰς τὴν γῆν ἣν ὤμοσεν αὐτοῖς, κατέστρωσεν αὐτοὺς ἐν τῇ ἐρήμῳ.
Ευδοκεω means to be pleased with or at.
Matthew 3:17 And behold [there came] a voice from heaven that said, This is my beloved Son, with whom I am well pleased [ευδοκησα].
It comes from the root sense of "to deem" (δοκεω) and the prefix ευ- meaning "well" or "good."
Καταστρεφω ("to overthrow") doesn't directly answer to the "slay" of Hebrew Numbers 14:16 (שחט), but is an interpretive translation; fundamentally, it just means "overthrow," as in Matthew 21:12:
Matthew 21:12 And Jesus entered the temple grounds and cast out all that were selling and buying therein, and the tables of the money changers he overturned [κατεστρεψεν], as well as the chairs of those that were selling doves.
It's probably best translated in LXX Numbers and 1 Corinthians by "laid waste to:" it implies a slaying but not explicitly so, like the Greek and unlike the Hebrew.
In 1 Corinthians 9-11, St. Paul is warning believers in God through Christ that those who believed in God through Moses but "fainted" (Revelation 2:3) or became "lukewarm," (Revelation 3:15-16; Matthew 24:12-13) or "commited fornication" (1 Corinthians 10:7-9 et seq.; Revelation 2:14-16, 20-23) are no more susceptible to the wrath of God than they—"the soul that sins, it shall die;" (Ezekiel 18:20) there are not Christians in name only.
1 Corinthians 9:23-27 (DRB)
And I do all things for the gospel's sake: that I may be made partaker thereof. 24 Know you not that they that run in the race, all run indeed, but one receiveth the prize? So run that you may obtain. 25 And every one that striveth for the mastery, refraineth himself from all things: and they indeed that they may receive a corruptible crown; but we an incorruptible one. 26 I therefore so run, not as at an uncertainty: I so fight, not as one beating the air: 27 But I chastise my body, and bring it into subjection: lest perhaps, when I have preached to others, I myself should become a castaway [αδοκιμος].
Here, St. Paul does not exempt himself in order to prove the rule: he runs to as to obtain, and not be "disqualified," or such as to be found "unfit" (αδοκιμος—"found unfit")—rendered elsewhere "reprobate." It's no surprise, then, that he goes on to say that many in the wilderness were not "pleasing" (αλλ ουκ εν τοις πλειοσιν αυτων ευδοκησεν—"but with the greater part of them he was not pleased"), or more literally, "found pleasing."
1 Corinthians 10:1-12 (DRB)
For I would not have you ignorant, brethren, that our fathers were all under the cloud, and all passed through the sea. 2 And all in Moses were baptized, in the cloud, and in the sea: 3 And did all eat the same spiritual food, 4 And all drank the same spiritual drink; (and they drank of the spiritual rock that followed them, and the rock was Christ.) 5 But with most of them God was not well pleased: for they were overthrown in the desert. 6 Now these things were done in a figure of us, that we should not covet evil things as they also coveted. 7 Neither become ye idolaters, as some of them, as it is written: The people sat down to eat and drink, and rose up to play. 8 Neither let us commit fornication, as some of them committed fornication, and there fell in one day three and twenty thousand. 9 Neither let us tempt Christ: as some of them tempted, and perished by the serpents. 10 Neither do you murmur: as some of them murmured, and were destroyed by the destroyer. 11 Now all these things happened to them in figure: and they are written for our correction, upon whom the ends of the world are come. 12 Wherefore he that thinketh himself to stand, let him take heed lest he fall.
The allusion to the Eucharist (or Lord's Supper) and to baptism is obviously intended to parallel the experience of the chosen people in the Old Covenant, and that partaking in these are not assurances to anyone in the New Covenant either. Indeed, St. Paul writes that unworthy reception of the Eucharistic elements had already resulted in the "overthrowal" and death of the congregation at Corinth:
1 Corinthians 11:23-32 (DRB) For I have received of the Lord that which also I delivered unto you, that the Lord Jesus, the same night in which he was betrayed, took bread. 24 And giving thanks, broke, and said: Take ye, and eat: this is my body, which shall be delivered for you: this do for the commemoration of me. 25 In like manner also the chalice, after he had supped, saying: This chalice is the new testament in my blood: this do ye, as often as you shall drink, for the commemoration of me. 26 For as often as you shall eat this bread, and drink the chalice, you shall shew the death of the Lord, until he come. 27 Therefore whosoever shall eat this bread, or drink the chalice of the Lord unworthily, shall be guilty of the body and of the blood of the Lord. 28 But let a man prove himself: and so let him eat of that bread, and drink of the chalice. 29 For he that eateth and drinketh unworthily, eateth and drinketh judgment to himself, not discerning the body of the Lord. 30 Therefore are there many infirm and weak among you, and many sleep. 31 But if we would judge ourselves, we should not be judged. 32 But whilst we are judged, we are chastised by the Lord, that we be not condemned with this world.
Then he goes on also to say that we have all been baptized like those in Moses were, in congruence with his example:
1 Corinthians 12:13 (DRB) For in one Spirit were we all baptized into one body, whether Jews or Gentiles, whether bond or free; and in one Spirit we have all been made to drink.
1 Corinthians 10:5
(KJV) But with many of them God was not well pleased [G2106]: for they were overthrown [G2693] in the wilderness.
G2106 Original: εὐδοκέω
Strong's Definition: From G2095 and G1380; to think well of, that is, approve (an act); specifically to approbate (a person or thing): - think good, (be well) please (-d), be the good (have, take) pleasure, be willing.
God was "not well pleased" here means He was displeased with them or their actions. He does not approve in wickedness or evil works instead He delights in righteousness.
Psalms 5:4 KJV For thou art not a God that hath pleasure in wickedness: neither shall evil dwell with thee.
Micah 7:18 KJV Who is a God like unto thee, that pardoneth iniquity, and passeth by the transgression of the remnant of his heritage? he retaineth not his anger for ever, because he delighteth in mercy.
Psalms 92:15 To shew that the LORD is upright: he is my rock, and there is no unrighteousness in him.
Romans 1:18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness;
G2693 Original: καταστρώννυμι
Part(s) of speech: Verb
Strong's Definition: From G2596 and G4766; to strew down, that is, (by implication) to prostrate (slay): - overthrow.
This "overthrow" was most closely refer to being struck down or slain.
Here are some related verses:
Numbers 26:65 KJV For the LORD had said of them, They shall surely die in the wilderness. And there was not left a man of them, save Caleb the son of Jephunneh, and Joshua the son of Nun.
"Die" here meaning,
Part(s) of speech: Verb
Strong's Definition: A primitive root; to die (literally or figuratively); causatively to kill: - X at all, X crying, (be) dead (body, man, one), (put to, worthy of) death, destroy (-er), (cause to, be like to, must) die, kill, necro [-mancer], X must needs, slay, X surely, X very suddenly, X in [no] wise.
Deuteronomy 9:28 KJV Lest the land whence thou broughtest us out say, Because the LORD was not able to bring them into the land which he promised them, and because he hated them, he hath brought them out to slay them in the wilderness.