A mother encounters worker, unyielding (7)
I believe the answer is:
adamant
'unyielding' is the definition.
(thesaurus)
'a mother encounters worker' is the wordplay.
'mother' becomes 'dam' (female parent of an animal).
'encounters' means one lot of letters go next to another.
'worker' becomes 'ant' (worker is a type of ant).
'a'+'dam'+'ant'='ADAMANT'
(Other definitions for adamant that I've seen before include "Firmly unchanging" , "Refusing to budge" , "Inflexible: fabulously hard rock" , "Refusing to change one's mind" , "With mind made up" .)