Funny tailless rodents hiding in the coal (7)
I believe the answer is:
comical
'funny' is the definition.
(synonyms)
'tailless rodents hiding in the coal' is the wordplay.
'tailless' means to remove the last letter (the tail of the word is removed).
'rodents' becomes 'mice' (mouse is a kind of rodent).
'hiding in' indicates putting letters inside.
'mice' with its final letter removed is 'mic'.
'mic' inserted within 'coal' is 'COMICAL'.
(Other definitions for comical that I've seen before include "Witty" , "Amusing or droll" , "'Amusing, funny (7)'" , "Causing laughter" , "Humorous" .)