Bread ingredient takes unknown direction (5)
I believe the answer is:
yeast
'bread ingredient' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'unknown direction' is the wordplay.
'unknown' becomes 'y' (algebra).
'direction' becomes 'east' (east is a kind of direction).
'y'+'east'='YEAST'
'takes' acts as a link.
Can you help me to learn more?
(Other definitions for yeast that I've seen before include "Brewing agent" , "Beer froth agent" , "Leavening agent in bread-making" , "Agent for making bread" , "Baker's raising agent" .)