(dated, UK, university slang) To close one's door as an indication that visitors are not welcome.

plural of one-line whip

A single-line whip.

(simile) Faithful to a promise one has made.

Alternative form of pick one's battles

To only involve oneself in disputes that one is likely to win. / To only take a stand for a cause that is truly important to one.

Contained in an official list (of members, employees, clients, projects etc.). / (business, accounting) Officially recorded in the financial records of a company or organization.

(idiomatic) To reveal one's real beliefs, sentiments, or character, especially through one's behavior.

Alternative form of show one's true stripes

To examine a situation, usually bad, from a positive perspective.