What line are you in?
What trade or profession are you of? “In the book line” —i.e. the book trade. This is a Scripture phrase. “The lines have fallen to
me in pleasant places, yea, I have a goodly heritage.” The allusion is
to drawing a line to mark out the lot of each tribe, hence line became
the synonym of lot, and lot means position or destiny; and hence a
calling, trade, or profession. Commercial travellers use the word
frequently to signify the sort of goods which they have to dispose of;
as, one travels “in the hardware line,” another “in the drapery line,” or “grocery line,” etc.
(The). The equator. (See Crossing The Line.)
The deep-sea line.
A long line marked at every five fathoms, for sounding the depth of
the sea. The line. All regiments of infantry except the
foot-guards, the rifle brigade, the marines, the militia, and the
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894