Secretary beginning to love mate (3)
I believe the answer is:
pal
'mate' is the definition.
(I've seen this in another clue)
'secretary beginning to love' is the wordplay.
'secretary' becomes 'PA' (abbreviation for personal assistant).
'beginning to' says to take the initial letters.
The initial letter of 'love' is 'l'.
'pa'+'l'='PAL'
(Other definitions for pal that I've seen before include "China" , "Close friend" , "Crony" , "Brother" , "Mate, informal friend" .)