Definition of bottom dead centre in English:

bottom dead centre

(US bottom dead center)

noun

  • A point in the cycle of a reciprocating engine, compressor, etc., when a piston is nearest the crankshaft and the corresponding crank is in line with its connecting rod; the position of the crank or piston at this point; (also) the point in pedalling a bicycle when one of the pedals is in the lowest position.

Origin

Late 19th century; earliest use found in Henry Evers (fl. 1850–1887).