A prefix denoting that the ingredient (of a compound) signified by the term to which it is prefixed,is present in only a small proportion, or less than the normal amount; as, subsulphide, suboxide, etc. Prefixed to the name of a salt it is equivalent to basic; as, subacetate or basic acetate.
SUB-
Meaning of SUB- in English
Webster's Revised Unabridged English Dictionary. Пересмотренный полный словарь английского языка Webster. 2012