Hooter in slow lane (3)
I believe the answer is:
owl
'hooter' is the definition.
(owls hoot)
'in slow lane' is the wordplay.
'in' indicates a hidden word.
'OWL' is hidden in the letters of 'slow lane'.
(Other definitions for owl that I've seen before include "Pussy-cat's wooer (Lear)" , "Nocturnal bird of prey" , "One swoops" , "Solemn person" , "Member of Parliament" .)