gui·tar (g?-tär?)n. A musical instrument having a flat-backed rounded body that narrows in the middle, a long fretted neck, and usually six strings, played by strumming or plucking.[French guitare, from Spanish guitarra, from Greek kithar?, cithara.]gui·tar?ist n.American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.