Ô

From Teflpedia

Ô (O-circumflex, lower case ô) is the letter O with a circumflex diacritic.

It's mostly used in English in French loanwords. In French it's indicative of elision of a historical S, which can be useful for cognate recognition; for example côte is a cognate with the English word coast, and French hôtel is a cognate of English hostel.