Old English stæf "walking stick, strong pole used for carrying, rod used as a weapon" (also, in plural, "letter, character, writing," cf. stæfcræft "grammar"), from Proto-Germanic *stabaz (cf. Old Saxon staf, Old Norse stafr, Old Frisian stef, Middle Low German and Middle Dutch staf, Old High German stab, German Stab, Gothic *stafs "element;" Middle Dutch stapel "pillar, foundation"), from PIE root *stebh- "post, stem, to support, place firmly on, fasten" (cf. Old Lithuanian stabas "idol," Lithuanian stebas "staff, pillar;" Old Church Slavonic stoboru "pillar;" Sanskrit stabhnati "supports;" Greek stephein "to tie around, encircle, wreathe," staphyle "grapevine, bunch of grapes;" Old English stapol "post, pillar").
Sense of "group of military officers that assists a commander" is attested from 1702, apparently from German, from the notion of the "baton" that is a badge of office or authority (a sense attested in English from 1530s). Meaning "group of employees (as at an office or hospital)" is first found 1837. Staff of life "bread" is from the Biblical phrase "to break the staff of bread" (Lev. xxvi:26), translating Hebrew matteh lekhem.
