thir·teen 
(thûr-tēn)
(thûr-tēn)n.
1. The cardinal number that is equal to the sum of 12 + 1.
2. The 13th in a set or sequence.
3. Something having 13 parts, units, or members.
[Middle English thyrtene, alteration of thrittene, from Old English thrēotīne; see trei- in the Appendix of Indo-European roots.]
thir·teen adj. & pron.