a composition, usu in verse, in which sets of letters, e.g. the first letter of each line, form a word or phrase
I had an acrostic once sent to me upon my name, which I was not at all pleased with — Jane Austen
a series of words of equal length arranged to read the same horizontally or vertically
[early French acrostiche from Greek akrostichis, from acro- + stichos line of verse]