Intent on listening.
1788. In the American Museum, iv. 565/2, “Aspasia” writes: Every time the door opens, or a foot is on the stairs, you are on the listen. On p. 567, “The Bachelor” points out that listen is “what we call a verb, not a substantive noun, as you have made it in that sentence.”
1803. They ’re always upon the listen in this house I think.—Mary Charlton, ‘Wife and Mistress,’ ii. 151. (N.E.D.)
