reservist
/rɛsərˈvɪst/Definitions
1. noun
A member of a military reserve or militia, especially one who is called up for active service in time of war or national emergency.
“The reservist had to adjust to a new schedule after being called up for duty.”
2. noun
A person who is employed or trained for a particular activity or profession outside of regular working hours.
“The IT reservist helped fix the server during the evening shift.”