A prefix signifying under, below, beneath, and hence often, in an inferior position or degree, in an imperfect or partial state, as in subscribe, substruct, subserve, subject, subordinate, subacid, subastringent, subgranular, suborn. Sub- in Latin compounds often becomes sum- before m, sur before r, and regularly becomes suc-, suf-, sug-, and sup- before c, f, g, and p respectively. Before c, p, and t it sometimes takes form sus- (by the dropping of b from a collateral form, subs-).
SUB-
Meaning of SUB- in English
Webster's Revised Unabridged English Dictionary. Пересмотренный полный словарь английского языка Webster. 2012