Forgets Tom is out (5)
I believe the answer is:
omits
'forgets' is the definition.
(I've seen this before)
'tom is out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'tom'+'is'='tomis'
'tomis' anagrammed gives 'OMITS'.
(Other definitions for omits that I've seen before include "misses out" , "Leaves out or neglects" , "skips" , "overlooks" , "Forgets" .)