# Are "Arc" and "Arch" interchangeable?

I've checked the dictionaries and both words have a common meaning:

arc - a shape or structure resembling an arc.

arch - a curved symmetrical structure spanning an opening and typically supporting the weight of a bridge, roof, or wall above it.

Can both these words be interchangeable?

• We went through the arc.
• We went through the arch.

Here is the Oxford Dictionary definition for arc that you referred to:

arc noun

1A part of a curve, especially a part of the circumference of a circle:
the point where a tangential line touches the arc of a circle

1.1 A shape or structure resembling an arc:
the huge arc of the sky

Note that, although definition 1.1 refers to a structure, the word arc in the following example (and in all of the other examples quoted) if followed by of. arc is not an actual structure: it serves only to define the shape of the real structure (the sky).

The definition in the Oxford dictionary would be better written as

the shape of a structure resembling an arc.

Here are the definitions from the Cambridge dictionary: as you can see, there is no (STRUCTURE) meaning for arc.

arc
noun [ C ] (CURVE) the shape of part of a circle, or other curved line.

arch
noun [ C ] (CURVED STRUCTURE) a structure, consisting of a curved top on two supports, that holds the weight of something above it.
noun [ C ] (SHAPE) something that has the shape of an arch, often used for decoration:

• @SovereignSun I would suggest that usage of arc is rather uncommon and is somewhat metaphorical in comparing the shape of a thing to the shape of a part of a circle - I would encourage you to look at the examples provided on your link. Generally an "arc" will not be understood to be a thing while an "arch" will be.
– Nat
Nov 28, 2016 at 9:59
• So they aren't interchangeable? Nov 28, 2016 at 10:04
• They are definitely not interchangeable. Nov 28, 2016 at 10:08
• @SovereignSun: Archangel and archbishop are from Ancient Greek ἄρχω ‎(árkhō): to lead. Archaeology and archaic are from Ancient Greek αρχαίος ‎(archaíos): ancient. Arch is from Latin arcus : a bow, arc, arch. So no, there is no connection. Nov 28, 2016 at 11:33

No. An arch (noun) suggests something that is connected to the ground, like the underside of a bridge or a tunnel. An arc (noun) can be free-floating.

• Do you have a citation for this claim? Is an arched window on the 100th floor "connected to the ground"? Nov 28, 2016 at 13:05
• Well, more broadly, it's in a vertical plane and standing on something, even if not the earth itself. Dec 6, 2016 at 17:33

I am a native French speaker, and a translator. I'd like to make a short terminology comparison. In English, for architecture, use arch, as in "pointed arch", in all cases. For geometry, use arc, or bow, like in bow-window.

In French, arc's first meaning is "bow" (cf. archer). Arche (Fr) is used to describe a large, primarily bow structure, typically in a bridge or a large space. But Arc (Fr) is just generic or for smaller construction elements. Pointed arch e.g. is said Arc Brisé (and not Arche). And for geometry as well it is Arc.

Exception: On Paris' Champs Élysees, you have the Arc de Triomphe, Rome has the Arc de Titus, which both are rather Arches (Fr) really by their dimensions, but for that kind of monument Arc is the traditionally used terminology. London has the Marble Arch.

And finally rainbow is said Arc-en-ciel (litt. a bow in the sky). How nice is that !

I hope this can somehow help & that no one will be upset this little linguistic invasion of mine.

• You should probably add for context that the English words roots are from the French words Arche and Arc Mar 23 at 6:34