1
general::
1. Also, in line with. In conformity or agreement; within ordinary or proper limits. For example, The new policy was intended to keep prices in line with their competitors, or It's up to the supervisor to keep the nurses in line. Also see FALL IN LINE. 2. Also, on line. Waiting behind others in a row or queue. For example, The children stood in line for their lunches, or There were at least 50 persons on line for opera tickets. 3. in line for. Next in order for, as in He is next in line for the presidency. All of these terms employ line in the sense of "an orderly row or series of persons or objects," a usage dating from the 1500s.
American Heritage Idioms
2
general::
Phrase(s): in line [and] on line
standing and waiting in a line of people. (On line is used especially in the New York City area.) • I’ve been in line for an hour. • Get in line if you want to buy a ticket. • We waited on line to see the movie.
McGrawhill's American Idioms And Phrasal Verbs