One that may be spotted laughing maniacally? (5)
I believe the answer is:
hyena
'one that may be spotted laughing maniacally?' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'one' is the wordplay.
I cannot really understand how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is found in the answer.
The remaining letters 'hyen' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
(Other definitions for hyena that I've seen before include "Carrion-eating mammal" , "Beast" , "Carrion-eating, dog-like animal" , "Carrion-feeding carnivore" , "Dog-like animal with laughter-like howl" .)