Lively Bohemian dance (5)
I believe the answer is:
'lively bohemian dance' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for polka that I've seen before include "Dance originally from part of 1 across" , "Dot may be associated with this" , "Folk dance" , "a merry dance?" , "Bohemian dance with three steps and a hop" .)