1 Sam 16:10 makes clear that Jesse had (at that time) eight sons with David being the youngest.
Thus Jesse made seven of his sons pass before Samuel, but Samuel told
him, “The LORD has not chosen any of these.”
11And Samuel asked him, “Are these all the sons you have?”
“There is still the youngest,” Jesse replied, “but he is tending the
However, 1 Chron 2:13-15 lists only seven sons with David still the youngest:
Jesse was the father of Eliab his firstborn; Abinadab was born second,
Shimeag third, Nethanel fourth, Raddai fifth, Ozem sixth, and David
Since 1 & 2 Chrinicles was (according to tradition) written by Ezra the Scribe after the Babylonian captivity, it is possible that one the eight sons died either of natural causes or in war.
Benson reaches the same conclusion:
David the seventh — David was certainly the youngest son of Jesse, 1
Samuel 16:11. And if, as seems probable, one of them died soon after
the time when they were said to he eight, he would of course be
reckoned as the seventh.
Similarly, the Pulpit commentary says:
Verses 13-15 give us what we have not elsewhere, the names of the
fourth, fifth, and sixth sons of Jesse, viz. Nathaneel, Raddai (but
see 1 Kings 1:8), and Ozem. But, on the other hand, they make it
appear that David was the seventh of seven, instead of (1 Samuel
14:10, 11; 1 Samuel 17:12) the eighth of eight sons. The missing son,
any way, belongs to the seventh place. The Syriac and Arabic versions
have taken the Elihu of 1 Chronicles 27:18, and put him in this place.
Others, following the Septuagint, suppose this Elihu, if strictly a
brother of David, to be Eliab, the oldest. The explanation of the
absence of the name here may be that he died early and without issue,
and would accordingly be the less wanted in a genealogical register. 1