Official has mum in for loan initially (6)
I believe the answer is:
formal
'official' is the definition.
(similar in meaning)
'mum in for loan initially' is the wordplay.
'mum' becomes 'ma' (ma can mean mother).
'in' means one lot of letters goes inside another.
'initially' suggests taking the first letters.
The first letter of 'loan' is 'l'.
'for'+'l'='forl'
'ma' inserted within 'forl' is 'FORMAL'.
'has' is the link.
(Other definitions for formal that I've seen before include "Conforming to accepted rules, as of dress" , "Essential" , "black tie" , "Ceremonial or stiffly polite" , "Not casual" .)