Sense there's agreement among a number (8)
I believe the answer is:
eyesight
'sense' is the definition.
(eyesight is a kind of sense)
'agreement among a number' is the wordplay.
'agreement' becomes 'yes'.
'among' is an insertion indicator.
'a number' becomes 'eight' (eight is a kind of number**).
'yes' inserted within 'eight' is 'EYESIGHT'.
'there's' acts as a link.
(Other definitions for eyesight that I've seen before include "Power of seeing" , "View" , "What's needed to see" , "Visual faculty" , "Requirement to look" .)