Plural of 'do', referring to hairstyles, or actions and duties you're supposed to perform; also things that are good or permissible.
'Do' as a hairstyle comes from 'do up' (to arrange), becoming common slang in the 1950s. As 'dos and don'ts', it comes from the verb 'do' meaning to perform, originating from Old English.
The fashion term 'do' really took off in the 1950s when elaborate hairdos became status symbols—and even today, 'dos and don'ts' is one of the few phrases where we use this old plural form regularly!
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