Guaiacum \Gua"ia*cum\, n. [NL., fr. Sp. guayaco, from native name in Hayti.] 1. (Bot.) A genus of small, crooked trees, growing in tropical America. 2. The heart wood or the resin of the {Guaiacum offinale} or lignum-vit[ae], a large tree of the West Indies and Central America. It is much used in medicine. [Written also {guaiac}.]