| OP | a military formation leaving enough space between ranks to allow an inspecting officer to pass |
|---|---|
| OP | a primary in which any registered voter can vote (but must vote for candidates of only one party) |
| OP | sandwich without a covering slice of bread |
| OP | something that is supposed to be secret but is generally known |
| OP | any very successful means of achieving a result |
| OP | a magical command |
| OP | a company whose workers are hired without regard to their membership in a labor union |
| OP | rear gunsight having an open notch instead of a peephole or telescope |
| OP | (`hospitable' is usually followed by `to') having an open mind |
| OP | (`capable' is usually followed by `of' or `to') possibly accepting or permitting |
| OP | (United Kingdom) a British university that is open to people without formal academic qualifications and where teaching is by correspondence or broadcasting or summer school |
| OP | make available, as of an opportunity |