The phrase "a side line" is correct and usable in written English.
It can be used to refer to a secondary activity or interest that is not the main focus, often related to work or hobbies.
Example: "While she works as a graphic designer, she also has a side line in photography."
Alternatives: "a side gig" or "a side hustle."
It's a side line of the information girls who give out West Side number They work at 435 West Fiftieth Street, and there have a teletype connection with the Weather Bureau's Battery office, and receive four complete weather reports a day.
As a side line he began importing materials… The N.Y.
A side line begins at the front wheel well and races up toward the tail.
As a side line he began importing materials for ballet costumes and to make the first silk tights and silk stocking in this country.
Nevertheless, it was the block's quirky charm and affordable rents that drew people like Mr. Rodgers, who has a side line as an independent filmmaker with a company called B1L Productions.
In fact, the most "inexperienced" member of that veteran five-a-side line-up was Fletcher, with 339 league appearances.
If you had told him then that in December 2014 he would be investing to convert an unprepossessing corner property at Didsbury into a restaurant, he would have pictured it as a side-line to his main project in life.
As a side-line contribution, due to the lack of rare species (e.g. singletons and doubletons), zeta diversity framework still allows us to extrapolate and estimate the number of species in the regional species pool (Fig. 5).
But opponents, including wildlife biologists and environmental groups, said the proposition was vaguely worded and they feared that it might lead to a side-lining of scientific advice.
It was not completely unlike the current Daria -- similar shape to the face, a different approach to the nose using a side-line instead of an underline and no glasses.
