The Collaborative International Dictionary of English v.0.48:
Siesta \Si*es"ta\, n. [Sp., probably fr. L. sessitare to sit much or long, v. freq. of sedere, sessum, to sit. See Sit.] A short sleep taken about the middle of the day, or after dinner; a midday nap. [1913 Webster]WordNet (r) 3.0 (2006):
siesta n 1: a nap in the early afternoon (especially in hot countries)