"to mark or fix the boundaries of," 1852, from French délimiter (18c.), from Late Latin delimitare "to mark out as a boundary," from de (see de-) + limitare, from limitem, limes "boundary, limit" (see limit (n.)). Related: Delimited; delimiting.
active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.
As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.
c. 1400, "boundary, frontier," from Old French limite "a boundary," from Latin limitem (nominative limes) "a boundary, limit, border, embankment between fields," which is probably related to limen "threshold," and possibly from the base of limus "transverse, oblique," which is of uncertain origin. Originally of territory; general sense from early 15c. Colloquial sense of "the very extreme, the greatest degree imaginable" is from 1904.