OXFORD 9000
📚 noun • entry_id 7929

keystone

/ˈkiː.stəʊn/
Meanings (ES + gloss)
clave • dovela
The top stone of an arch.
The tunnel, which is 1,000 yd. long, had been closed to passenger traffic since November 17, 1949, after some of the keystones had worked loose.
Word forms