From The Collaborative International Dictionary of English v.0.48 [gcide]:
3. (Arch.) (a) A brick or stone laid with its shorter face or head in the surface of the wall. (b) In framing, the piece of timber fitted between two trimmers, and supported by them, and carrying the ends of the tailpieces.
5. A fall or plunge head first, as while riding a bicycle, or a skateboard, or in bathing; -- sometimes, implying the striking of the head on the ground; as, to take a header. [Colloq.] [PJC] Headfirst
From WordNet (r) 3.0 (2006) [wn]:
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