(education) Referring to exams in which external resources such as textbooks, glossaries, study notes, calculators, etc. may be used.

(idiomatic) Something of which salient aspects are obvious or easily interpreted.

plural of open cluster

plural of open book

plural of open compound

(uncountable) A chess opening characterized by the moves 1.e4 e5, in which both White and Black move their king's pawn to the fourth rank with their first move.

(television) An opening segment shown before the opening credits.

plural of cold open

A device for putting a hole in a pipe. / A device or mechanism for clearing obstructions in a pipe. / (sports) A practice event; a warm-up.

simple past tense and past participle of open fire