Lively motor returned by end of January (4)
I believe the answer is:
racy
'lively' is the definition.
(I've seen this before)
'motor returned by end of january' is the wordplay.
'motor' becomes 'car' (informal term for car).
'returned' shows that the letters should be reversed in order.
'by' means one lot of letters go next to another.
'end of' says to take the final letters.
The last letter of 'january' is 'y'.
'car' written backwards gives 'rac'.
'rac'+'y'='RACY'
(Other definitions for racy that I've seen before include "Suggestive; spirited" , "bawdy quality" , "Sexually suggestive" , "Risqu" , "rather blue" .)