Nick's typist possibly sitting on terrace (7)
I believe the answer is:
tempter
'nick's typist' is the definition.
The definition suggests a singular noun which matches the answer.
'possibly sitting on terrace' is the wordplay.
'possibly' becomes 'temp' (I can't explain this - if you can you should believe this answer much more).
'sitting on' is a charade indicator (letters next to each other).
'terrace' becomes 'ter' (I've seen this in other clues).
'temp'+'ter'='TEMPTER'
Can you help me to learn more?
(Other definitions for tempter that I've seen before include "The Devil?" , "One offering enticement" , "Satan" , "Siren" , "Enticer" .)