He wasnt there, but sent a busy worker round (8)
I believe the answer is:
absentee
'he wasnt there' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'sent a busy worker round' is the wordplay.
'busy worker' becomes 'bee' (I've seen this in another clue).
'round' means one lot of letters goes inside another.
'a'+'bee'='abee'
'sent' put within 'abee' is 'ABSENTEE'.
'but' is the link.
Can you help me to learn more?
(Other definitions for absentee that I've seen before include "One failing to attend" , "Someone not present" , "Bunker" , "to prompt a hearty increase in affection!" , "shirker?" .)