Permit enclosed grabbed by parasites (7)
I believe the answer is:
licence
'permit' is the definition.
(I know that permit can be written as licence)
'enclosed grabbed by parasites' is the wordplay.
'enclosed' becomes 'enc' (abbreviation for 'enclosed' as in letters).
'grabbed by' means one lot of letters goes inside another (inserted letters are grabbed inside).
'parasites' becomes 'lice' (lice are parasitic insects).
'enc' put within 'lice' is 'LICENCE'.
(Other definitions for licence that I've seen before include "Authority (or the lack of it!)" , "Self-indulgence; permit" , "Driving permit" , "Official permit" , "Permit - excessive behaviour" .)