Underground drain hasn't rain around entry (5)
I believe the answer is:
debut
'entry' is the definition.
(I know that entry can be written as debut)
'underground drain hasn't rain around' is the wordplay.
'underground' becomes 'tube' (the London Underground is nicknamed the Tube).
'hasn't' is a deletion indicator.
'around' shows that the letters should be reversed in order.
'drain' with 'rain' taken out is 'd'.
'tube'+'d'='tubed'
'tubed' in reverse letter order is 'DEBUT'.
(Other definitions for debut that I've seen before include "First attempt" , "The coming out of a society girl" , "opening" , "Initial appearance" , "First public appearance of performer" .)