Manic killer, hacks when cycling outside yard (6)

I believe the answer is:

psycho

I'm a little stuck... Click here to teach me more about this clue!

'manic' is the definition.
(thesaurus)

I cannot understand how the remainder of the clue works.

(Other definitions for psycho that I've seen before include "Well-known Hitchcock film" , "1960 horror film" , "unstable person" , "Bates Motel horror film" , "Alfred Hitchcock thriller" .)

I've seen this clue in The Hindu.

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