Holiday shower under bar (8)
I believe the answer is:
restrain
'bar' is the definition.
(I've seen this before)
'holiday shower under' is the wordplay.
'holiday' becomes 'rest' (I've seen this before).
'shower' becomes 'rain' ('rain shower' can be a synonym of 'shower').
'under' says to put letters next to each other.
'rest'+'rain'='RESTRAIN'
(Other definitions for restrain that I've seen before include "bottle up" , "Stop" , "Hold back, tether" , "Arrest - confine - subdue" , "Keep in check" .)