Source : Webster's Revised Unabridged Dictionary (1913)

Singlet \Sin"glet\, n.
   An unlined or undyed waistcoat; a single garment; -- opposed
   to {doublet}. [Prov. Eng.]

Source : WordNet®

singlet
     n : a collarless men's undergarment for the upper part of the
         body [syn: {vest}, {undershirt}]