acronym (n.)

word formed from the first letters of a series of words, 1943, American English coinage from acro- + -onym "name" (abstracted from homonym; ultimately from PIE root *no-men- "name"). With the exception of cabalistic esoterica and acrostic poetry, this way of forming words was exceedingly uncommon before 20c. For distinction of usage (regretfully ignored on this site), see initialism.