Why is the ninth month called September?
Old English faldan (Mercian), fealdan (West Saxon), transitive, "to bend cloth back over itself," class VII strong verb (past tense feold, past participle fealden), from Proto-Germanic *falthan, *faldan (cf. Middle Dutch vouden, Dutch vouwen, Old Norse falda, Middle Low German volden, Old High German faldan, German falten, Gothic falþan).
The Germanic words are from PIE *pel-to- (cf. Sanskrit putah "fold, pocket," Albanian pale "fold," Middle Irish alt "a joint," Lithuanian pleta "I plait"), from root *pel- (3) "to fold" (cf. Greek ploos "fold," Latin -plus).
The weak form developed from 15c. In late Old English also of the arms. Intransitive sense, "become folded" is from c.1300 (of the body or limbs); earlier "give way, fail" (mid-13c.). Sense of "to yield to pressure" is from late 14c. Related: Folded; folding.
"pen or enclosure for sheep or other domestic animals," Old English falæd, falud "stall, stable, cattle-pen," a general Germanic word (cf. East Frisian folt "enclosure, dunghill," Dutch vaalt "dunghill," Danish fold "pen for sheep"), of uncertain origin. Figurative use by mid-14c.
"a bend or ply in anything," mid-13c., from fold (v.).
fold 1 (fōld)
A crease or ridge apparently formed by folding, as of a membrane; a plica.
In the embryo, a transient elevation or reduplication of tissue in the form of a lamina.
an enclosure for flocks to rest together (Isa. 13:20). Sheep-folds are mentioned Num. 32:16, 24, 36; 2 Sam. 7:8; Zeph. 2:6; John 10:1, etc. It was prophesied of the cities of Ammon (Ezek. 25:5), Aroer (Isa. 17:2), and Judaea, that they would be folds or couching-places for flocks. "Among the pots," of the Authorized Version (Ps. 68:13), is rightly in the Revised Version, "among the sheepfolds."