Assert old medical condition limits resistance (5)
I believe the answer is:
argue
'assert' is the definition.
(thesaurus)
'old medical condition limits resistance' is the wordplay.
I cannot really see how this works, but
'resistance' could be 'r' (electronics abbreviation) and 'r' is present in the answer.
'condition' could be 'ague' (ague is a kind of condition) and 'ague' is found in the leftover letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for argue that I've seen before include "Discuss, contend" , "Dispute, express angry words" , "Dispute - debate" , "Contest verbally, dispute" , "express disagreement" .)