I am reserved, but lewd (8)
I believe the answer is:
immodest
'lewd' is the definition.
(thesaurus)
'i am reserved' is the wordplay.
'i am' becomes 'I'm' (contraction).
'reserved' becomes 'modest' (I've seen this before).
'im'+'modest'='IMMODEST'
'but' is the link.
(Other definitions for immodest that I've seen before include "Brazen" , "Indecent, indecorous" , "Swift proposal was not" , "Not seemly or decently dressed" , "blowing its own trumpet" .)