Add in hint about date (7)
I believe the answer is:
include
'add' is the definition.
(including is a kind of adding)
'in hint about date' is the wordplay.
'hint' becomes 'clue' ('clue' can be a synonym of 'hint'**).
'about' indicates putting letters inside.
'date' becomes 'd' (common abbreviation eg in DOB, date of birth).
'clue' enclosing 'd' is 'clude'.
'in'+'clude'='INCLUDE'
(Other definitions for include that I've seen before include "Cover" , "Enclose or comprise as a part" , "Admit" , "Contain - embrace" , "Allow participation in" .)