The operative word in Prov 30:5 is אּמְרַת (imrah = "word"/"utterance"/"speech") which occurs 37 times in the OT and 19 times just in Ps 119 alone where it is often used almost equivalently to "Torah"/"law" or commandment of God; and only 11 times outside the psalms.
"The Complete Word Study Dictionary Old Testament" (Baker & Carpenter) offers the following comments on this poetic word (the word occurs almost exclusively in Hebrew poetry):
It is used in parallel with teaching, covenant, commandment and voice
(Deut 32:2, 33:9, Ps 119:172, Isa 28:23). The noun most often
designates God's Word, which is the psalmist's guide for life and his
basis for requesting God's kindness, graciousness and deliverance (Ps
119:11, 41, 58, 76, 133, 154, 170). The keeping of God's Word is a
frequent topic of Scripture (Deut 33:9, Ps 119:67, 158; cf. Isa 5:24).
God's Word is pure, sweeter than honey, and has been magnified with
His name (Ps 119:103, 138:2, Prov 30:5).
The OP's question about the breadth of this noun's meaning is simple - anything that God says which includes:
- a message specifically given by (say) a prophet to a specific recipient (eg, see 2 Sam 12)
- the Torah
- God's Word as contained in the Canon of Scripture
- God's creative word (eg, Gen 1, Prov 30:4)
- God's nature as revealed in our natural surroundings and His creation
- the Law, etc.
Note the comments of Ellicott:
(5) Every word of God is pure.—Comp. Psalms 19, where first
(Proverbs 30:1-6) the glories of God as revealed in nature are
described, and then (Proverbs 30:7 sqq.) the excellence of the
revelation of Himself in His word is extolled. Every word of God is
“pure,” i.e., tested and proved in the furnace of experience; e.g.,
His promise to be a “shield” (Genesis 15:1) to those that trust in
Him. (Comp. Psalm 18:30.)
APPENDIX - Hebrew Words for "Word"
There are several words translated "word" in the OT which includes:
- אֵמֶר (emer) = speech word, eg, Gen 49:21, Num 24:4, + 46 others
- אֹמֶר (omer) = promise, speech thing word, eg, Job 22:28, Ps 19:2, 3, 68:11, 77:8, Hab 3:9
- אִמְרָה (imrah) = utterance, speech, word, eg, Gen 4:23, Deut 32:2, 9 + 34 others
- דָבָר (dabar) = speech, word, eg, Gen 11:1, 12:17, 15:1, + 1438 others
- מִלָּה (millah) = word, speech, eg, 2 Sam 23:2, Job 4:2, 4, + 36 others
Possibly the closest to word in meaning (they all overlap in meaning) to the Greek "logos" and "rhema" is the Hebrew דָבָר (dabar), but they are not identical.