(idiomatic) A complex, troublesome situation arising when a decision or action produces considerable subsequent problems.

Known but not quite remembered.

(idiomatic) Talking a lot, especially without saying anything of value or meaning.

(idiomatic) To go extinct or become obsolete; to fall out of common practice or use; to become a thing of the past.

A book, containing blank pages, in which people may sign their name and write a short message as a symbol of sympathy; often in response to a high-profile death or series of deaths.

(relativity) The principle that only the motion of objects relative to one another can be measured, and that there is no absolute frame of reference.

(American spelling, idiomatic) An unrelated or only incidentally related matter with distinctly different significance.

(idiomatic, formulaic) A minimal level of competence or effectiveness, as used in phrases where one is unable to perform.

(idiomatic, informal) A very long time; a period regarded as too long.

Used other than figuratively or idiomatically: see off, top, head. / (idiomatic) In an extemporaneous manner; without careful thought, preparation, or investigation.