Probably from ashar; increase -- flock.
see HEBREW ashar
H6251. ashtaroth
II. [עַשְׁתָּרוֺת] noun plural feminine only construct in phrase נ֑ךָ צאֶֹ עַשְׁתְּר(וֺ)ת Deuteronomy 7:13; 28:4, 18, 51 (all "" אֲלָפֶיךָ שְׁגַר) usually interpreted either as
a. = ewes (Thes) or as
b. = young (compare veneres gregis; in either case with reference to ±Aštart as goddess of fecundity; RSSemitic i. 292, 457 f., 2nd ed. 310, 476 f., adopting b, thinks one type of ±Ašt in Canaan had form of sheep, so DrDeuteronomy 7:13); compare also as name of land fertilized by dew and rain WeSkizzen iii. 170.