Motor, serviceable at last, to give hoot (4)
I believe the answer is:
care
'give hoot' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'motor serviceable at last' is the wordplay.
'motor' becomes 'car' (informal term for car).
'at last' suggests the final letters.
The last letter of 'serviceable' is 'e'.
'car'+'e'='CARE'
'to' is the link.
Can you help me to learn more?
(Other definitions for care that I've seen before include "Race (anag.)" , "Guardianship; anxiety" , "See 16" , "Serious attention and thought" , "Prudence" .)