Group of Chicago CSI detectives going over nightclub (5)
I believe the answer is:
disco
'nightclub' is the definition.
(a disco is a club for dancing)
'group of chicago csi detectives going over' is the wordplay.
'group of' indicates a hidden word (group of letters from the clue).
'going over' says the letters should be written backwards.
'ocsid' is hidden in the letters of 'chicago csi detectives'.
'ocsid' back-to-front is 'DISCO'.
(Other definitions for disco that I've seen before include "lively entertainment, for some?" , "Place to dance to recorded music, in short" , "Nightclub with dancing to recorded music" , "Modern dance hall or event, in brief" , "Dance hall - music by Donna Summer and the Bee Gees, say" .)