Happening to be seventy without clothing (5)
I believe the answer is:
event
'happening' is the definition.
(I've seen this in other clues)
'seventy without clothing' is the wordplay.
'without clothing' indicates the central letters (the two letters which clothe the rest are removed).
The centre of 'seventy' is 'EVENT'.
'to be' is the link.
(Other definitions for event that I've seen before include "Incident, occurrence" , "Thing that happens" , "A thing taking place" , "ride competitively" , "horse-riding competition" .)