Poisonous, masculine rodent with empty nest (10)
I believe the answer is:
malevolent
'poisonous' is the definition.
(similar in meaning)
'masculine rodent with empty nest' is the wordplay.
'masculine' becomes 'male' (similar in meaning).
'rodent' becomes 'vole' (vole is a kind of rodent).
'with' says to put letters next to each other.
'empty' means to remove the middle letters.
'nest' with its centre removed is 'nt'.
'male'+'vole'+'nt'='MALEVOLENT'
(Other definitions for malevolent that I've seen before include "Evil-minded" , "Spiteful" , "mean-spirited" , "Ill-disposed towards others" , "Wishing evil to others" .)