sub- Also suc-, suf-, sug-, sup-, sur-, and sus-.
A lower level or position; somewhat or nearly; secondary action.
[Latin sub, under, close to, to some degree.]
This is a common prefix, both in words which have come from Latin with it already attached, and also in many examples coined in English.
One set contains the literal idea of something moving to or being at a lower level or position, as in submarine, subconscious, subcutaneous (Latin cutis, skin), substratum, and subtitle; this leads into a sense of being lower in rank, of secondary status, or a part of something larger: subaltern, subcommittee, subhuman, sublieutenant, subordinate, subculture, subframe, subset, suburb.
A second set contains the idea of something imperfect or incomplete, which suggest that a thing is less than, somewhat, or nearly like another: subarctic, subclinical, subequatorial, submarginal, sub-orbital, subsonic.
In some verbs (and associated nouns) the prefix marks a later or secondary action of the same kind: subcontract, sublet, subdivide. It can be used informally to suggest something is in an inferior version of another style: sub-Wordsworthian, sub-Marxist. In chemistry, sub- is included in the names of compounds containing a relatively small proportion of a component, as in suboxide.
Some examples where sub- became attached in Latin, and in which it has a figurative association in English, include subdue (ducere, to lead or draw); sublime (in which the second element may be related to limen, threshold); subscribe (scribere, to write); subjugate (jugum, yoke); submit (mittere, to send, put); and subsequent (sequi, to follow).
Several variant forms of the prefix occur before certain consonants in words adopted from Latin. It becomes suc- before c: succinct (cingere, to gird); suf- before f: suffocate (fauces, throat); sug- before g: suggest (gerere, to bring); sup- before p: support (portare, to carry); sur- before r: surreptitious (rapere, to seize), but see also sur-; sus- before c, p, or t: susceptible (capere, to take), suspend (pendere, to hang), sustain (tenere, to hold).