Know beforehand said number understand (7)
I believe the answer is:
foresee
'know beforehand' is the definition.
(I've seen this in another clue)
'said number understand' is the wordplay.
'said' indicates a 'sounds like' (homophone) clue.
'number' becomes 'four' (four is a kind of whole number).
'understand' becomes 'see' (synonyms).
'four' is a homophone of 'fore'.
'fore'+'see'='FORESEE'
(Other definitions for foresee that I've seen before include "Expect" , "Imagine" , "Prognosticate" , "To know beforehand" , "witness in advance?" .)