The word was used figuratively as early as the late 17th century; The Winthrop Papers records a 1692 usage of “the tenterhooks of expectation” by G. In Roderick Random (1748) Tobias Smollett writes: Eventually such explanatory phrases became elliptically understood, leaving us with the now common on the anxious seat In a state of apprehension or suspense; in a state of difficulty or doubt.The figurative expression derives from the literal anxious seat or bench, or mourners’ bench, of American revivalist camp meetings, on which penitents desirous of forgiveness and seeking conversion were wont to sit while anxiously awaiting the call or sign of salvation.The term was used in its still current figurative sense early in this century:on the rack Under great pressure or strain; in painful suspense or acute psychological torment; on tenterhooks; tense, anxious, nervous.The rack, a former instrument of torture, consisted of a frame with rollers at either end to which the victim’s ankles and wrists were attached in order to stretch his joints.
(Psychology) psychol a state of intense apprehension or worry often accompanied by physical symptoms such as shaking, intense feelings in the gut, etc, common in mental illness or after a very distressing experience.
Since the 17th century this term has been applied figuratively to a person’s thoughts and feelings that affect the overall color or tone of his mood.
Thus “key up” is to heighten, intensify, or stimulate a cat in a strange garret Uneasy, nervous; fearful, afraid.
Taut strings are also more brittle and thus more likely to break.keyed up Excited, high-strung; nervous, tense; intensified, stimulated; psyched up (for), full of nervous energy and anticipation.
The verb key refers literally to tuning a musical instrument —that is, raising or lowering the pitch.