Sarah to become fatigued and cross (7)
I believe the answer is:
saltire
'cross' is the definition.
(saltire is a kind of cross)
'sarah to become fatigued' is the wordplay.
'sarah' becomes 'sal' (Sally is a common pet form of Sarah).
'to become fatigued' becomes 'tire' (I've seen this before).
'sal'+'tire'='SALTIRE'
'and' acts as a link.
(Other definitions for saltire that I've seen before include "The Scottish flag" , "X-shaped cross" , "Diagonal cross (heraldry)" , "Heraldic cross" , "flag - 8's? [SAINT ANDREW]" .)