City beginning to sicken pale marine (7)
I believe the answer is:
swansea
'city' is the definition.
(Swansea is an example)
'beginning to sicken pale marine' is the wordplay.
'beginning to' suggests taking the first letters.
'pale' becomes 'wan' (wan can mean pale or grey).
'marine' becomes 'sea' (both can mean 'of the sea').
The first letter of 'sicken' is 's'.
's'+'wan'+'sea'='SWANSEA'
(Other definitions for swansea that I've seen before include "Welsh port" , "Second city of Wales" , "Home of the DVLA" , "Welsh city" , "South Wales city" .)