That is either fully on or fully off, and is used to toggle a status between on and off; as in an on-off switch / That fluctuates between a positive and negative status, as an on-off relationship

(Classical linguistics, in definite) The dative case in its use to indicate purpose. / (uncommon, Classical linguistics, countable) A specific use of the dative case in this way.

(idiomatic) Death; or a place or period where death is impending. / (idiomatic) A place of great danger.

(calculus) An unspecified constant term added to a particular antiderivative to make it represent its whole family of antiderivatives, usually denoted with C.

A relative measure of the quality of life a person or group has, often with per capita income (GNI or GDP) serving as a proxy measurement but with some notion of human development as the real (underlying) entity being measured.

A proposed office of the future, where computers and software have made paper unnecessary.

Non-Oxford British English standard spelling of water of crystallization.

(idiomatic) In suspense; waiting eagerly or anxiously for some resolution.

Adjectival or attributive form of angels dancing on the head of a pin.

(figuratively) The subject of arcane intellectual speculation; used as an example subject of enquiry the pursuit of which is of no value.