Reach that is very limited by pain (7)
I believe the answer is:
achieve
'reach' is the definition.
(synonyms)
'that is very limited by pain' is the wordplay.
'that is' becomes 'i.e.' (short for Latin 'id est', 'that is').
'very' becomes 'v' (abbreviation).
'limited by' means one lot of letters goes inside another (limit can mean to contain or border off).
'pain' becomes 'ache' (ache is a kind of pain).
'ie'+'v'='iev'
'iev' going inside 'ache' is 'ACHIEVE'.
(Other definitions for achieve that I've seen before include "wrap up" , "Reach or accomplish" , "'Accomplish, attain (7)'" , "Bring about by effort" , "Successfully bring off" .)