Merriam-Webster Collegiate Dictionary - acrostic

 noun  Etymology: Middle French & Greek; Middle French ~he, from Greek akrostichis, from akr- acr- + stichos line; akin to steichein to go — more at stair  Date: 1530  1. a composition usually in verse in which sets of letters (as the initial or final letters of the lines) taken in order form a word or phrase or a regular sequence of letters of the alphabet  2. acronym  • ~ also ~al adjective  • ~ally adverb