Silly lapse catching English out (6)
I believe the answer is:
asleep
'out' is the definition.
(I've seen this before)
'silly lapse catching english' is the wordplay.
'silly' indicates an anagram.
'catching' is an insertion indicator.
'english' becomes 'e' (abbreviation).
'lapse' with letters rearranged gives 'aslep'.
'aslep' enclosing 'e' is 'ASLEEP'.
(Other definitions for asleep that I've seen before include "Napping" , "Snoozing" , "not paying attention" , "this fast?" , "Dead to the world" .)