castellation
noun
cas·tel·la·tion
ˌkastəˈlāshən
plural -s
1
: the act of castellating
2
: a castellated structure
3
a
: battlement
b
: a groove or recess in a castellated structure (as a nut)
a cotter pin passing through the castellation and the hole in the bolt
Word History
Etymology
Medieval Latin castellation-, castellatio, from castellatus + -ion, -io -ion