He’s positive I stop Tim working (8)
I believe the answer is:
optimist
'he's positive' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'i stop tim working' is the wordplay.
'working' is an anagram indicator.
'i'+'stop'+'tim'='istoptim'
'istoptim' with letters rearranged gives 'OPTIMIST'.
Can you help me to learn more?
(Other definitions for optimist that I've seen before include "One always sees the glass as half-full" , "One looking on bright side" , "One always tends to take a favourable view of things" , "One always believes the glass is half-full" , "One who always looks on the positive side" .)