varletyoudaoicibaDictYouDict[varlet 词源字典]
varlet: [15] Varlet and valet [16] are doublets – they come from the same ultimate source. This was Vulgar Latin *vassus, a borrowing from Old Celtic *wasso- ‘young man, squire’. From *vassus were derived two medieval Latin diminutive forms: vassallus, which has given English vassal [14], and *vassellitus. This passed into Old French as vaslet, which diversified into valet (source of English valet) and varlet (source of English varlet).

Both to begin with retained their original connotations of a ‘young man in service to a knight’, and hence by extension any ‘feudal retainer or servant’, but while valet still denotes a ‘servant’, varlet went down in the world in the 16th century to ‘knave’.
=> valet, vassal[varlet etymology, varlet origin, 英语词源]
varlet (n.)youdaoicibaDictYouDict
mid-15c., "servant, attendant of a knight," from Middle French varlet (14c.), variant of vaslet, originally "squire, young man," from Old French vassal (see vassal). The meaning "rascal, rogue" is 1540s.