Clear and then let out plant (6)
I believe the answer is:
nettle
'plant' is the definition.
The answer is an example.
'clear and then let out' is the wordplay.
'clear' becomes 'nett' (similar in meaning).
'and then' means one lot of letters go next to another (I've seen this in other clues).
'out' means to remove the last letter.
'let' with its last letter taken off is 'le'.
'nett'+'le'='NETTLE'
(Other definitions for nettle that I've seen before include "Sting or annoy with the plant" , "Plant to irritate" , "To be annoying" , "urticaceous plant" , "Grasp it firmly and it will not sting" .)