Agreed old reduction in food shortage by date (2,1,4)
I believe the answer is:
of a mind
'agreed' is the definition.
(I've seen this before)
'old reduction in food shortage by date' is the wordplay.
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'reduction in' means to remove the last letter (the number of letters in the word is reduced).
'food shortage' becomes 'famine' (I've seen this before).
'by' is a charade indicator (letters next to each other).
'date' becomes 'd' (abbreviation e.g. dob - date of birth).
'famine' with its final letter taken off is 'famin'.
'o'+'famin'+'d'='OF A MIND'
(Other definitions for of a mind that I've seen before include "In accord" , "Agreed" .)