ETYM Greek akrostichis; acro extreme + stichos order, line, verse.
Verse in which certain letters such as the first in each line form a word or message.
A number of lines of writing, usually verse, whose initial letters (read downward) form a word, phrase, or sentence. A single acrostic is formed by the initial letters of lines only; a double acrostic is formed by the first and last letters.

A puzzle where one fills a square grid with words reading the same down as across; SYN. acrostic.

In the form of an acrostic