KEYSTONED
Verb
keystoned
simple past tense and past participle of keystone
Adjective
keystoned (not comparable)
Having a keystone.
a keystoned arch
Source: Wiktionary
KEYSTONE
Key"stone`, n. (Arch.)
Definition: The central or topmost stone of an arch. This in some styles is
made different in size from the other voussoirs, or projects, or is
decorated with carving. See Illust. of Arch. Keystone State, the
State of Pennsylvania; -- so called from its having been the central
State of the Union at the formation of the Constitution.
Source: Webster’s Unabridged Dictionary 1913 Edition