1. A crown worn as a sign of royalty.
2. Royal power or dignity.
tr.v. di·a·demed, di·a·dem·ing, di·a·dems
Middle English diademe, from Old French, from Latin diadma, from Greek, band, from diadein, to bind around : dia-, dia- + dein, d-, to bind.
Not so, when diadem'd with rays divine. --Pope.
To terminate the evil, To diadem the right. --R. H. Neale.