From an unused root meaning to glisten (or be green); grass (or any tender shoot) -- grass, herb.
H6212. eseb
עֵ֫שֶׂב noun masculineGenesis 1:11 herb, herbage; — ׳ע absolute Deuteronomy 11:15 +; construct Genesis 2:5 +; suffix עֶשְׂבָּם Isaiah 42:15; plural construct עִשְּׂבוֺת (dagesh forte dirimens) Proverbs 27:25; — herb, herbage, in oldest use often General (therefore including grass [דֶּשֶׁא]): ׳ע הַשָּׂדֶה Exodus 9:22 (E), Genesis 2:5 (+ שִׂיחַ) Exodus 9:25 (+ עֵץ), 10:15 (+ id; all J) Amos 7:2, so ׳ע הָאָרֶץ Exodus 10:12 (E), + הָעֵץ מְּרִי 10:15 (J), whence Psalm 105:35; apparently Generally also in ׳ע הארץ Job 5:25; Psalm 72:16, ׳ע alone 92:8; ׳ע כָּלהַֿשָּׂדֶה Jeremiah 12:14, ׳ע alone Deuteronomy 32:2 ("" דֶּשֶׁא), Isaiah 42:15; Psalm 102:5; 102:12, and Deuteronomy 29:22; Micah 5:6; Proverbs 19:12; hence ׳ע as food for cattle Deuteronomy 11:15; Psalm 106:20 compare Jeremiah 14:6; Zechariah 10:1; הָרִים עִשְּׂבוֺת Proverbs 27:25 ("" חָצִיר דֶּשֶׁא,); but as human food (hence excluding דֶּשֶׁא) ׳ע הַשָּׂדֶה Genesis 3:18 (J); especially P 1:29 (+ עֶץ), ע ׳יֶרֶק 1:30; 9:3, hence ׳ע Psalm 104:14 ("" חָצִיר for cattle); ׳ע distinguished from עֵץ דֶּשֶׁא, also Genesis 1:11-12, ׳ע שָׂדֶה + חָצִיר דֶּשֶׁא, 2 Kings 19:26 + Isaiah 37:27.