Mother stands up, fuming
I believe the answer is:
mad
'fuming' is the definition.
(I've seen this in another clue)
'mother stands up' is the wordplay.
'mother' becomes 'dam' (female parent of an animal).
'stands up' says the letters should be written backwards (in a down clue, letters go up).
'dam' written backwards gives 'MAD'.
(Other definitions for mad that I've seen before include "(Of a dog) rabid" , "Crazed" , "Angry or insane" , "Insane - furious" , "like the March Hare" .)