Words known to change about old hack with unusual limitations (10)
I believe the answer is:
vocabulary
'words' is the definition.
(thesaurus)
'known to change about old hack with unusual limitations' is the wordplay.
I cannot really understand how this works, but
'about' could be 'ca' (abbreviation for circa) and 'ca' is present in the answer.
'old' could be 'o' (abbreviation) and 'o' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for vocabulary that I've seen before include "Knowledge of words" , "List of words" , "Words an individual knows" , "Range of words" , "Word list" .)