Source : Webster's Revised Unabridged Dictionary (1913)

Sestet \Ses*tet"\, n. [It. sestetto, fr. sesto sixth, L. sextus,
   fr. sex six.]
   1. (Mus.) A piece of music composed for six voices or six
      instruments; a sextet; -- called also {sestuor}. [Written
      also {sestett}, {sestette}.]

   2. (Poet.) The last six lines of a sonnet.

Source : WordNet®

sestet
     n 1: the cardinal number that is the sum of five and one [syn: {six},
           {6}, {VI}, {sixer}, {sise}, {Captain Hicks}, {half a
          dozen}, {sextet}, {sextuplet}, {hexad}]
     2: six performers or singers who perform together [syn: {sextet},
         {sextette}]
     3: a set of six similar things considered as a unit [syn: {sextet},
         {sextette}]
     4: a musical composition written for six performers [syn: {sextet},
         {sextette}]
     5: a rhythmic group of six lines of verse