Splendid secretary who’s been in the family a long time? (7)
I believe the answer is:
grandpa
'who's been in the family a long time?' is the definition.
'splendid secretary' is the wordplay.
'splendid' becomes 'grand' (I've seen this in other clues).
'secretary' becomes 'pa' (I've seen this in other clues).
'grand'+'pa'='GRANDPA'
(Other definitions for grandpa that I've seen before include "Parent's father" , "Relation" , "Pop" , "Drag pan over to the elder" , "family member" .)