רֵאשִׁית having the sense of "preeminent" or "best"

  

. . . the term “first” (rē’šīt) may also be qualitative, meaning the preeminent or the best, as in Jer 49;35; Amos 6:6; Prov 3:9; and Dan 11:41. (C. L. Seow, “Revisiting Behemoth,” in Biblical Essays in Honor of Daniel J. Harrington, SJ, and Richard J. Clifford, SJ: Opportunity For No Little Instruction, ed. Christopher G. Frechette, Christopher R. Matthews, and Thomas D. Stegman [New York: Paulist Press, 2014], 49)

 

The third definition for רֵאשִׁית is

 

first, best: r¢°šît °ônî first of my strength = firstborn Gn 49₃; r¢°šît gôyyim Nu 24₂₀; r¢°šît kol-minµâ 1S 2₂₉;

 

We have the following from TDOT:

 

3. Best. In Am. 6:6 rēʾšîṯ probably means simply “the best,” with no reference to firstfruits: “You anoint yourselves with the finest oils.” The same is true in Jer. 49:35: “I am going to break the bow of Elam, their strongest (rēʾšîṯ) weapon”; and 1 S. 15:21: “From the spoil, the people took sheep and cattle, the best (rēʾšîṯ) of the things devoted to destruction, to sacrifice to the Lord your God in Gilgal.” Nu. 24:20 has a play on words involving rēʾšîṯ and ʾaḥ^arîṯ: “First/best among the nations was Amalek, but its end (ʾaḥ^arîṯô) is to perish forever.” (S. Rattray and J. Milgrom, “רֵאשִׁית,” in Theological Dictionary of the Old Testament, ed. G. Johannes Botterweck, Helmer Ringgren, and Heinz-Josef Fabry, 15 vols. [Grand Rapids, Mich.: Eerdmans 2004], 13:271)