It quite alters one's meaning (3)
I believe the answer is:
not
'quite alters one's meaning' is the definition.
I can't tell whether this defines the answer.
'it' is the wordplay.
I cannot really understand how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is located in the answer.
The remaining letters 'no' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for not that I've seen before include "Negation of what follows" , "Negatory word" , "A negative word" , "logically, operation needed" , "It negates a word" .)