1. A number of lines of writing, especially a poem or word puzzle, in which particular letters, e.g., the first in each line, spell a word or phrase: An acrostic is a short composition in which the initial letters of the lines, taken in order, spell a word, phrase, or sentence. Sometimes the last or middle letters of the lines, or all of them, are similarly arranged to spell words, etc., whence a distinction of single, double, or triple acrostics.

A verse or arrangement of words in which certain letters in each line, such as the first or last when taken in order, spell out a word, motto, etc.
2. A Hebrew poem in which the consecutive lines or verses begin with the successive letters of the alphabet; The twelve of the Psalms are considered to be acrostic. The Psalm cxix. is thought to be the best example.

Pertaining to a poem written in a special way using the initial letters of the lines: Mrs. Smart explained to her English class that they were to compose a poem in an acrostic style, in which certain letters, normally the first in each line, form a name, a message or a motto when read in succession.