Shake Bert and Mel off (7)
I believe the answer is:
tremble
'shake' is the definition.
(I know that shake can be written as tremble)
'bert and mel off' is the wordplay.
'and' means one lot of letters go next to another.
'off' indicates anagramming the letters.
'bert' after 'mel' is 'melbert'.
'melbert' anagrammed gives 'TREMBLE'.
(Other definitions for tremble that I've seen before include "quail" , "Shiver slightly as with cold" , "Look nervous" , "Shake - quiver" , "Show fear" .)