Complete by about ten to one again (6)
I believe the answer is:
entire
'complete' is the definition.
('entire' can be a synonym of 'complete')
'about ten to one again' is the wordplay.
'about' is an anagram indicator.
'to one' becomes 'i' (Roman numeral).
'again' becomes 're'.
'ten' with letters rearranged gives 'ent'.
'ent'+'i'+'re'='ENTIRE'
'by' acts as a link.
(Other definitions for entire that I've seen before include "Lure" , "Envelope" , "porter" , "outright" , "in one piece" .)