a. (UN-1 7 b.)

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1832.  Miss Mitford, Our Village, Ser. V. 278. An old bonnet,… so twisted … that its pristine shape was unguessable.

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1865.  Dublin Univ. Mag., I. 266. There are passages … the meaning whereof … is to me unknowable, unguessable. [Common in recent use.]

3