Chief knowing structure of bridge, say (4)
I believe the answer is:
arch
This clue is a quadruple definition!!
'chief' is the first definition.
('arch' can be a synonym of 'chief')
'knowing' is the second definition.
(thesaurus)
'structure' is the third definition.
(arch is a kind of structure)
'of' is a link.
'bridge say' is the fourth definition.
'arch' can be an answer for 'bridge' (thesaurus). I am unsure of the 'say' bit.
Can you help me to learn more?
(Other definitions for arch that I've seen before include "Chief - part of foot" , "Inner part of foot" , "(archaic)" , "Affectedly playful (4)" , "Waggish" .)