Origin and history of improvision

late 14c., provisioun, "foresight, prudence, care;" also "a providing beforehand, action of arranging in advance" (at first often in reference to ecclesiastical appointments made before the position was vacant), from Old French provision "precaution, care" (early 14c.), from Latin provisionem (nominative provisio) "a foreseeing, foresight, preparation, prevention," noun of action from past-participle stem of providere "look ahead" (see provide).

The meaning "something provided, supply of necessary things" is attested from mid-15c.; specific sense of "supply of food" (provisions) is by c. 1600. In law, "a stipulation, a distinct clause in a statute, etc.; a rule or principle," late 15c. A provision-car (by 1864) was a railroad car with refrigeration for preserving perishable products during transportation.

word-forming element meaning "not, opposite of, without" (also im-, il-, ir- by assimilation of -n- with following consonant, a tendency which began in later Latin), from Latin in- "not," cognate with Greek an-, Old English un-, all from PIE root *ne- "not."

In Old French and Middle English often en-, but most of these forms have not survived in Modern English, and the few that do (enemy, for instance) no longer are felt as negative. The rule of thumb in English has been to use in- with obviously Latin elements, un- with native or nativized ones.