I am in about the frost (4)
I believe the answer is:
rime
'the frost' is the definition.
('rime' can be a synonym of 'frost')
'i am in about' is the wordplay.
'i am' becomes 'i'm'.
'in' indicates putting letters inside.
'about' becomes 're' (common abbreviation for 'with reference to').
'im' placed into 're' is 'RIME'.
(Other definitions for rime that I've seen before include "dated poetry" , "''The ... of the Ancient Mariner'' (Coleridge)" , "Frost left after freezing fog, or frozen dew" , "Hoar frost" , "Type of frost" .)