Out of adjustment or alignment, not working properly. Kilter is an American variant of kelter, an English dialect word used since the seventeenth century to mean “in good condition.” James Lowell used it in an 1862 letter, “I must rest awhile. My brain is out of kilter.” The origin of the synonymous out of whack, dating from the late 1800s, is more mysterious. The OED suggests it may come from wacky, for “crazy,” but that is by no means certain. Both terms are used to describe malfunctioning mechanisms (“This tape recorder is out of kilter and won’t rewind”) as well as figuratively (“He may have a conscience, but if you ask me, it’s slightly out of whack”).