The principal activity in your life that you do to earn money(noun)
WordNet. Princeton University. 2010.
Use "line of work" in a sentence
"A few days before his death he came to Governor's Island for the purpose of ascertaining in what line of work he could be most useful in building up sound public opinion in favor of such preparedness as would give us a real peace-insurance."
"Maybe because of your line of work you know this man, Mr. Lemand said."
"Her value in this line of work is difficult to imagine; against a submerged U-boat, she could do nothing; had she been asked to confront Derfflinger or any other German battle cruiser sent into the North Atlantic, her lot would have been martyrdom."