Distractedly omits riddle, being terribly absent-minded (6)
I believe the answer is:
scatty
'absent-minded' is the definition.
(I've seen this before)
'distractedly omits riddle being terribly' is the wordplay.
'omits' indicates named letters should be taken away.
'being terribly' indicates an anagram.
'distractedly' with 'riddle' taken out is 'stacty'.
'stacty' with letters rearranged gives 'SCATTY'.
(Other definitions for scatty that I've seen before include "Slightly crazy" , "dizzy" , "Disorganised, unpredictable" , "Not thinking straight" , "Slangily crazy or scatterbrained" .)