Weird in the cheeriest way (5)
I believe the answer is:
eerie
'weird' is the definition.
(both can mean strange or unsettling)
'in the cheeriest way' is the wordplay.
'in' indicates the answer is hidden within the clue.
'EERIE' is hidden within 'cheeriest way'.
(Other definitions for eerie that I've seen before include "Weird and disturbing" , "Mysterious" , "Frighteningly odd" , "Scary, weird" , "Weird, uncanny" .)