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Old English dysig "foolish, stupid," from Proto-Germanic *dusijaz (cf. Low German düsig "dizzy," Dutch duizelen "to be dizzy," Old High German dusig "foolish," German Tor "fool," Old English dwæs, Dutch dwaas "foolish"), perhaps from PIE *dheu- (1) "dust, vapor, smoke; to rise in a cloud" (and related notions of "defective perception or wits").
Meaning "having a whirling sensation" is from mid-14c.; that of "giddy" is from c.1500 and seems to merge the two earlier meanings. Used of the "foolish virgins" in early translations of Matthew xxv; used especially of blondes since 1870s. Related: Dizzily.
Old English dysigan, from source of dizzy (adj.). Related: Dizzied; dizzying.
early 14c., from Old French deien (12c., Modern French doyen), from Late Latin decanus "head of a group of 10 monks in a monastery," from earlier secular meaning "commander of 10 soldiers" (which was extended to civil administrators in the late empire), from Greek dekanos, from deka "ten" (see ten). Replaced Old English teoðingealdor. College sense is from 1570s (in Latin from late 13c.).
Silly; foolish; inane; ditzy •Found as a noun meaning ''foolish man'' by 1825; now mostly used of women, and esp, since the 1870s, of blondes: some dizzy broad (1501+)