An engaging thing to do (4)
I believe the answer is:
hire
This clue might be a double definition.
'an engaging thing' is the first definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'do' is the second definition.
The definition and answer can be both to do with social activities as well as being verbs in their base form.
Maybe there's an association between them I don't understand?
'to' is the link.
Can you help me to learn more?
(Other definitions for hire that I've seen before include "Rent or lease" , "Pay for temporary use" , "Payment for use" , "Rent, employ" , "Employ (for wages)" .)