UK, 1951—‘mother-in-law’s chair’, ‘mother-in-law’s cushion’ and ‘mother-in-law’s seat’ are colloquial appellations for the globular spiny cactus Echinocactus grusonii, native to Mexico
conventionally middle-class—UK, 1953—from ‘Mrs Dale’, the name of a conventional middle-class woman in Mrs Dale’s Diary, a BBC radio serial broadcast from 1948 to 1969
looking or feeling ill or nauseated—1843, in a letter by Charles Dickens—when applied to a person, the plural noun ‘gills’ designates the flesh under the jaws and ears; also the cheeks
everyone is accountable for their own actions—17th century—may refer to herrings being hung when up for sale (that is to say: every piece of merchandise must sell on its own merits)