a prefix from the latin preposition cum, signifying with, together, in conjunction, very, etc. it is used in the form com- before b, m, p, and sometimes f, and by assimilation becomes col- before l, cor- before r, and con- before any consonant except b, h, l, m, p, r, and w. before a vowel com- becomes co-; also before h, w, and sometimes before other consonants.