These words refer to anything the times have passed by because of its age, inefficiency or displacement by something superior, or because of changing tastes. Old-fashioned suggests that something has gone out of use because of an arbitrary change of custom: old-fashioned thick stockings for women. The word can also suggest a change in technology rather than in taste: old-fashioned 78 rpm records. But it does not necessarily imply that the outmoded or superseded thing in question no longer exists physically: the old-fashioned wedding dress she had treasured for 20 years. Sometimes the word can nostalgically describe something valued for its quaintness, its formality or its wholesome simplicity: the current rage for old-fashioned coach and ship lamps; an old-fashioned wedding with all the trimmings; plain, old-fashioned home cooking.

Out-of-date and passé share with old-fashioned an emphasis on an arbitrary change of taste and style. Out-of-date is descriptive and neutral and may refer to a lack of factual validity as well as to a change of taste; passé carries a tinge of contempt for something no longer in vogue statistics that rapidly become out-of-date ; full of passé notions about which hair styles are chic and sophisticated.

Antediluvian , meaning literally before the Flood, is a hyperbole for ideas more neutrally expressed by antiquated and archaic . Antiquated suggests the continued existence of something very old and now functioning badly, if not also superseded long ago by a more efficient or useful arrangement: an antiquated , treadle-operated sewing machine. Archaic may also suggest something old but still surviving; in this sense, it implies a given period in the past and can be used solely to classify rather than to evaluate: the archaic dress of the Amish Mennonites; a statue carved in the archaic manner. In other senses, archaic refers to something extremely old and not now in general use; in this case it can be a more formal or technical substitute for old-fashioned : many archaic declensions that were abandoned during the development of the language. The hyperbolic antediluvian is mostly used humorously for any of these meaning of antiquated or archaic , with the added suggestion, when it pertains to ideas, of an extremely conservative or reactionary temper: an economic policy as antediluvian as a troglodyte.

Obsolete and obsolescent refer to different moments in the same process. Obsolete indicates what has already passed totally from use or adherence or what has been completely superseded; obsolescent points to what is now passing away: The death penalty for theft has long been obsolete , but for graver crimes it is only now becoming obsolescent . Obsolescent has a special reference, as well, to arbitrary modifications of a product that are deliberately introduced not to increase its usefulness but to make earlier models seem passé : Motor-cars, like women’s clothes, are now designed to become obsolescent in a single year.

Obsolete , obsolescent and archaic are all applied to words that are now seldom or never used. An obsolete word is no longer used either in speech or writing, usually because it has been supplanted by a different word. "Oscitate," meaning to yawn, is now obsolete . An obsolescent word, though still in use, is becoming obsolete . Much modern slang rapidly becomes obsolescent . Archaic words were current at some time in the past, and appear in literature and in the Bible; unlike obsolete words they are still used, either for effect, because they have an unmistakable flavour of their period or milieu, or else by persons whose vocabularies were formed in a distinctively earlier era. The word "methinks" and the phrase "I trow" are archaic .