/therr"teenth"/ , adj.
1. next after the twelfth; being the ordinal number for 13.
2. being one of 13 equal parts.
n.
3. a thirteenth part, esp. of one ( 1 / 13 ).
4. the thirteenth member of a series.
[ bef. 900; THIRTEEN + -TH 2 ; r. ME thrittenthe (see THREE, TENTH), OE thrytteotha (see TITHE) ]