single: [14] Single comes via Old French sengle or single from Latin singulus. This was formed from sim-, the stem of simplus ‘single’ (which came from the same Indo-European base that produced English same and similar), together with the diminutive suffix *-go and a further element *-lo. Singlet ‘vest’ [18] was coined on the model of doublet, in allusion to its being an unlined garment, made from a ‘single’ layer of material. => same, similar, simple[single etymology, single origin, 英语词源]