Bridge opponents, in boring style, overlooking some altogether (8)
I believe the answer is:
entirely
'altogether' is the definition.
('entirely' can be a synonym of 'altogether')
'bridge opponents in boring style overlooking some' is the wordplay.
'bridge opponents' becomes 'en' (I've seen this in other clues).
'in boring style' becomes 'tiresomely'.
'overlooking' is a deletion indicator.
'tiresomely' with 'some' taken out is 'tirely'.
'en'+'tirely'='ENTIRELY'
(Other definitions for entirely that I've seen before include "Wholly and completely" , "'Fully, wholly (8)'" , "Altogether" , "Wholly, completly" , "Fully or absolutely" .)