abbr.

early 15c., abbreviacioun, "shortness; act of shortening; a shortened thing," from Old French abréviation (15c.) and directly from Late Latin abbreviationem (nominative abbreviatio), noun of action from past-participle stem of abbreviare "shorten, make brief," from Latin ad "to" (see ad-) + breviare "shorten," from brevis "short, low, little, shallow" (from PIE root *mregh-u- "short").

From 1580s specifically of words. Technically a part of a word, usually the initial letter or syllable, used for the whole word but with no indication of the rest of the word (as abbr. for abbreviation or abbreviate). A contraction is made by elision of certain letters or syllables from the body of a word but still indicates its full form (as fwd. for forward; rec'd. for received).