Thirteen is ten plus three, and a great many people will tell you it is unlucky.
The superstition is old and stubborn, and it has a name, triskaidekaphobia. Hotels skip the thirteenth floor, aircraft skip the row, and Friday the thirteenth has an entire film series to itself. Whether anybody genuinely believes it is another matter. The word has a useful opposite in the baker's dozen, which is thirteen and was said to be an extra loaf added so the baker could not be accused of short measure.
1nounthirteenThe number after twelve.
“She turned thirteen in the spring.”
Thirteen has swapped its letters round. Old English þrēotīene was simply three plus ten, and Middle English thrittene became thirteen by metathesis, the same shuffle that turned thritty into thirty.
Proto-Germanic
*þritehun
Old English
þrēotīene
Middle English
thirttene
English, today
thirteen
Built from
From Middle English thirttene, variant (through metathesis) of thrittene, from Old English þrēotīene, from Proto-Germanic þritehun, compound of þrīz (“three”) + tehun (“teen”). Cognate with West Frisian trettjin, Dutch dertien, German dreizehn, Danish tretten. Equivalent to three + -teen.
Etymology from Wiktionary, CC BY-SA