The Collaborative International Dictionary of English v.0.48:

Lubricant \Lu"bri*cant\, a. [L. lubricans, p. pr. of lubricare,
   See Lubricate.]
   Lubricating.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lubricant \Lu"bri*cant\, n.
   That which lubricates; specifically, a substance, as oil,
   grease, graphite, etc., used for reducing the friction of the
   working parts of machinery.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lubricant
    n 1: a substance capable of reducing friction by making surfaces
         smooth or slippery [syn: lubricant, lubricator,
         lubricating substance, lube]