Pussy keeps heading for cream? I'm not sure (7)
I believe the answer is:
sceptic
'i'm not sure' is the definition.
(a sceptic is unsure or doubtful about things)
'pussy keeps heading for cream?' is the wordplay.
'pussy' becomes 'septic' (ie full of pus).
'keeps' indicates putting letters inside.
'heading for' indicates taking the first letters.
The initial letter of 'cream' is 'c'.
'septic' enclosing 'c' is 'SCEPTIC'.
(Other definitions for sceptic that I've seen before include "One inclined to question accepted opinions" , "One questioning accepted opinions" , "He's hard to convince" , "Thomas for one" , "One who doubts accepted opinions" .)