Old section in Heritage Dictionary (4)
I believe the answer is:
aged
'old' is the definition.
(similar in meaning)
'section in heritage dictionary' is the wordplay.
'section' says the answer is hidden in the clue.
'AGED' is hidden in the letters of 'in heritage dictionary'.
(Other definitions for aged that I've seen before include "Got older" , "Elderly" , "Old or ancient" , "well over the hill" , "Became older" .)