One in unusual stress doesn't give in (7)
I believe the answer is:
resists
'one in unusual stress doesn't give in' is the definition.
I can't judge whether this definition defines the answer.
'one in unusual stress' is the wordplay.
'one' becomes 'I' (Roman numeral).
'in' means one lot of letters goes inside another.
'unusual' indicates an anagram.
'stress' with letters rearranged gives 'ressts'.
'i' going inside 'ressts' is 'RESISTS'.
Can you help me to learn more?
(Other definitions for resists that I've seen before include "Is reluctant" , "Fights back" , "Defends" , "Defies" , "Sisters (anag.)" .)