Acrostic
2 of the 7 encyclopedias on this shelf carry an entry for Acrostic. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a composition so arranged that the initial letters of the lines taken in order spell out some name, title, or motto, or follow the order of the alphabet. An acrostic may be written in such a way that the final letters or, indeed, any letters, have a similar effect. Edgar A. Poe is credited with an acrostic so framed that the first letter of the first line, the second letter of the second line, the third letter of the third line, etc., formed the name Francis Sargent Osgood. Addison (see Spectator No. 60), considered the maker of an acrostic a mere blockhead, saying, "I have seen some of them where the verses have not only been edged by a name at every extremity, but have had the same name running down like a seam through the middle of the poem." One of the most famous acrostics in history was formed in the time of Charles II. Some wit noted that the names of the ministers, Clifford, Ashley, Buckingham, Arlington, and Lauderdale, could be arranged in such a way that their initials formed the word cabal, a term signifying low political intrigue. The word cabal has ever since had additional significance. It is now taken to mean a junta or clique of persons organized for some questionable purpose. Psalm cxix is an acrostic. In the original Hebrew the initial letters of the divisions form the alphabet. The juvenile jingle, "A apple pie; B baked it; C cut it," etc., is a familiar nursery acrostic.
Collier's New Encyclopedia (1921)
a poetical composition, disposed in such a manner that the initial letters of each linc, taken in order, form a person's name or other complete word or words. This kind of poetical triflings was very popular with the French poets from the time of Francis I. until Louis XIV. THE ACROPOLIS AT ATHENS, AS IT WAS IN THE TIME OF PERICLES In the Old Testament there are 12 psalms written according to this principle. Of these, the 119th Psalm is the most remarkable; it consists of 22 stanzas, each of which commences with a Hebrew letter, and is called by its name. Acrostic animals, they are called also animal verse is no longer cultivated by the poets. Edgar Allan Poe wrote some striking acrostics, varying the form with great ingenuity,