Arbitrary component of error and omission (6)
I believe the answer is:
random
'arbitrary' is the definition.
(thesaurus)
'component of error and omission' is the wordplay.
'component of' indicates the answer is hidden within the clue (I've seen this in other clues).
'RANDOM' is hidden in the letters of 'error and omission'.
(Other definitions for random that I've seen before include "Without a particular aim, haphazard as choice may be" , "without any plan" , "Lacking a pre-planned pattern" , "can be hit-and-miss" , "Without order" .)