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naff [naff 词源字典]: naff: [20] There seem to be two separate words naff in British slang, but the origins of both are mysterious. The first, naff off, appeared in the 1950s. Functionally it is a euphemistic substitute for fuck off, and there could be some connection with eff, another euphemism for fuck (perhaps the n in an eff wandered out of place). Alternatively it could come from naf, an old backslang reversal of fan in the sense ‘female genitals’.

The second, an adjective meaning ‘unstylish, unfashionable, tasteless’, is first recorded in 1969. Its antecedents are even more obscure. Among possible relatives are northern English dialect niffy-naffy ‘stupid’ and naffy, naffin and naffhead ‘idiot’ and Scots nyaff ‘unpleasant person’.
[naff etymology, naff origin, 英语词源]
dysfunctional (adj.): 1917, from dysfunction + -al (1). Related: Dysfunctionally.
functional (adj.): 1630s, "pertaining to function or office," from function (n.) + -al (1), or from Medieval Latin functionalis. Meaning "utilitarian" is by 1864; specific use in architecture is from 1928. Related: Functionally; functionality.