Ballroom dance of Cuban origin (5)
'ballroom dance of cuban origin' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for rumba that I've seen before include "music one can dance to" , "number of steps" , "South American dance" , "Lively Cuban dance" , "Umbra (anag)" .)
(Another definition for rhumba that I've seen is " Latin dance (alt sp)".)