i Register
In some senses, sideline is marked as figuratively. Watch for register when choosing this word.
ADJ
lucrative, nice (little), profitable, useful
She runs a profitable sideline selling handmade jewelry online alongside her main job.
VERB + SIDELINE
have | develop
PREP
~ for
Selling homemade jewelry online is a useful sideline for extra income.
~ in
My uncle has built up a profitable sideline in repairing old bicycles.
~ to
His wife runs a small jewelry business as a sideline to her full-time job.