Look dance up (4)
I believe the answer is:
leer
'look' is the definition.
(I know that leer is a type of look)
'dance up' is the wordplay.
'dance' becomes 'reel' (reel is a kind of dance).
'up' is a reversal indicator (in down clue: letters go upwards).
'reel' back-to-front is 'LEER'.
(Other definitions for leer that I've seen before include "Give sly look" , "Gaze lasciviously at" , "Ogle, smirk" , "Give lascivious look" , "Suggestive or sneering look" .)