This year it’ll be 245 years in employment (5)
I believe the answer is:
usage
'employment' is the definition.
(synonyms)
'this year it'll be 245 years' is the wordplay.
I cannot really see how this works, but
'years' could be 'age' (synonyms) and 'age' is located in the answer.
The remaining letters 'us' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
'in' acts as a link.
Can you help me to learn more?
(Other definitions for usage that I've seen before include "Common practice" , "Habit" , "Utilisation" , "Usual practice" , "Tradition - rate of consumption" .)