pointed, round, rounded
brick, steel, stone, etc.
monumental (esp. BrE), triumphal
Gothic, Romanesque, etc.
proscenium
a performance space with a traditional proscenium arch

railway (BrE)
Homeless people slept under the railway arches.

graceful
the graceful arches of the bridge

build, erect
This huge triumphal arch was erected at the beginning of this century.

form, make
The branches of the trees formed an arch over the bench.

beneath an/the arch, through an/the arch, under an/the arch
He rode under the arch.

Arch is used with these nouns as the subject:
back, eyebrow

Arch is used with these nouns as the object:
back, brow, eyebrow