“Gratis” not right if this applies (3)
I believe the answer is:
fee
'this applies' is the definition.
The definition suggests a singular noun which matches the answer.
'gratis not right' is the wordplay.
'gratis' becomes 'free' (synonyms).
'not' indicates named letters should be taken away.
'right' becomes 'r' (common abbreviation).
'free' with 'r' taken away is 'FEE'.
'if' acts as a link.
Can you help me to learn more?
(Other definitions for fee that I've seen before include "Cost" , "Money paid for professional services" , "Amount paid for job" , "Sum payable to professional person for services" , "Charge for professional services" .)