Thalamus \Thal"a*mus\, n.; pl. {Thalami}. [L. thalamus chamber, Gr. qa`lamos.] 1. (Anat.) A mass of nervous matter on either side of the third ventricle of the brain; -- called also {optic thalamus}. 2. (Bot.) (a) Same as {Thallus}. (b) The receptacle of a flower; a torus.