The Collaborative International Dictionary of English v.0.48:

Ragtime \Rag"time`\, n. (Mus.)
   a rhythm with a regular accompaniment in two-four time and a
   melody characterized by syncopation, first recognized in many
   negro melodies; also a style of American music in this
   rhythm.
   [Webster 1913 Suppl. +PJC] Raguled

WordNet (r) 3.0 (2006):

ragtime
    n 1: music with a syncopated melody (usually for the piano)
         [syn: ragtime, rag]

Moby Thesaurus II by Grady Ward, 1.0:

54 Moby Thesaurus words for "ragtime":
   acid rock, andante tempo, avant-garde jazz, ballroom music, beat,
   bebop, boogie-woogie, bop, compound time, country rock,
   dance music, dances, duple time, folk rock, hard rock, hot,
   hot jazz, jazz, jazzed up, jazzy, jive, largo, mainstream jazz,
   march tempo, mixed times, musical suite, presto, rag, ragtimey,
   rhythm-and-blues, rock, rock-and-roll, rubato, sextuple time,
   simple time, suite, suite of dances, swing, swingy, syncopated,
   syncopated music, syncopation, syncope, tempo, tempo rubato,
   the new music, three-quarter time, time, time pattern, timing,
   triple time, triplet, two-four time, waltz time