Once a year naked habit? (8,4)
I believe the answer is:
birthday suit
'naked habit?' is the definition.
(being in your 'birthday suit' means being naked)
'once a year' is the wordplay.
I cannot really see how this works, but
'a' is found in the answer.
'year' could be 'y' and 'y' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for birthday suit that I've seen before include "Nothing to wear?" , "Invisible attire?" , "Invisible threads?" , "Invisible outfit?" , "State of being unclothed" .)