know B from a battledore

• know a B from a battledore

know B from a battledore (third-person singular simple present knows B from a battledore, present participle knowing B from a battledore, simple past knew B from a battledore, past participle known B from a battledore)

1. (archaic, often in the negative) To know anything at all; to have the most basic common sense or intelligence.
   • [1599, [Thomas] Nashe, “To His Readers, Hee Cares Not What They Be”, in Nashes Lenten Stuffe, […], London: […] [Thomas Judson and Valentine Simmes] for N[icholas] L[ing] and C[uthbert] B[urby] […], →OCLC:

     Euery man can ſay Bee to a Battledore, and write in prayſe of Vertue, and the ſeuen Liberall Sciences, threſh corne out of the full ſheaues, and fetch water out of the Thames; but out of drie ſtubble to make an after harueſt, and a plentifull croppe without ſowing, and wring iuice out of a flint, thats Pierce a Gods name, and the right tricke of a workman.]

• know A from B
• (vulgar, UK) know one's arse from one's elbow
• (vulgar, US) know one's ass from a hole in the ground