Real Dictionary

guitar
variable noun: A guitar is a musical instrument with six strings and a long neck. You play the guitar by plucking or strumming the strings.

guitar in American English
a musical instrument related to the lute but having a flat back and usually six strings that are plucked or strummed with the fingers or a plectrum
noun: a stringed musical instrument with a long, fretted neck, a flat, somewhat violinlike body, and typically six strings, which are plucked with the fingers or with a plectrum

guitar in British English
noun: a plucked stringed instrument originating in Spain, usually having six strings, a flat sounding board with a circular sound hole in the centre, a flat back, and a fretted fingerboard. Range: more than three octaves upwards from E on the first leger line b