[one-night stand] {n. phr.} 1. A single performance given by a […]

[one-two] {n.} 1. A succession of two punches, the first a […]

[one-upmanship] {v.}, {informal} Always keeping ahead of others; trying to keep […]

[onion] See: [KNOW ONE'S WAY AROUND] (2).

[only] See: [HAVE EYES ONLY FOR], [IF ONLY].

[open] See: [EYES OPEN, THROW OPEN].

[open and aboveboard] {adj. phr.} Honest. * /Jacob felt that the […]

[open and shut] See: [CUT AND DRIED].

[open arms] See: [RECEIVE WITH OPEN ARMS].

[open fire] {v. phr.} To begin shooting. * /The big warship […]