1. a prefix occurring originally in loanwords from Latin ( subject; subtract; subvert; subsidy ); on this model, freely attached to elements of any origin and used with the meaning "under," "below," "beneath" ( subalpine; substratum ), "slightly," "imperfectly," "nearly" ( subcolumnar; subtropical ), "secondary," "subordinate" ( subcommittee; subplot ).
2. Chem.
a. a prefix indicating a basic compound: subacetate; subcarbonate; subnitrate.
b. a prefix indicating that the element is present in a relatively small proportion, i.e., in a low oxidation state: subchloride; suboxide.
Also, su-, suc-, suf-, sug-, sum-, sup-, sur-, sus- .
[ sub (prep.); akin to Gk hypó; see HYPO- ]