acrostic (n.)

short poem in which the initial letters of the lines, taken in order, spell a word or phrase, 1580s, from Medieval Latin acrostichis, from Greek akrostikhis, from akros "at the end, outermost" (from PIE root *ak- "be sharp, rise (out) to a point, pierce") + stikhos "line of verse," literally "row, line," from PIE root *steigh- "to stride, step, rise" (see stair). The second element is properly -stich, but it has been assimilated to workds in -ic. As an adjective from 1680s.