Queen weighed down by too much fur (5)
I believe the answer is:
otter
'fur' is the definition.
(otter is a kind of fur)
'queen weighed down by too much' is the wordplay.
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'weighed down by' means one lot of letters go next to another (in a down clue, some letters go on top of others).
'too much' becomes 'OTT' (short for over the top).
'er' after 'ott' is 'OTTER'.
(Other definitions for otter that I've seen before include "furry creature" , "Freshwater mammal with dark brown fur" , "Water animal with webbed fee, brown fur and flat tail" , "river in Honiton" , "Water mammal" .)