What is the word for the corner where ceiling and wall meet in a house?

Question

In a square room in a house, what is the word for the corner where one of the walls meets the ceiling?

I kept thinking it was a word like "eaves", but that turned out to be the overhang. I have googled a few things, but most of it is irrelevant about topics like mold.

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Edit, for clarity:

In math, two distinct planes may intersect on a line, and 3 distinct planes may intersect at a point. Lines segments between two points are sometimes called edges.

I said "square room", but what technically meant was "cube room".

I said "corner where one of the walls meet the ceiling" because I was thinking of the phrase, "Stand with his nose in the corner." I've heard the word "corner" refer to BOTH the line of intersection between two planes AND the point of intersection between 3 planes, when people talk about rooms. As in, "Painting yourself into a corner."

I should have used the word "edge", because I've only heard "edge" referred to as the LINE of intersection between two planes. I think of "edge" as a more specialized word, for someone doing graph theory or geometry. "Edge" would have been a much better word to use in asking because of the reduced ambiguity.

To be most clear, the reason I accepted the answer is because of the word crown. Crown can be used to distinguish the difference between the edges where the walls meet the ceiling vs where the walls meet the floor.

I'm sorry for the confusion.

Answer 1

The terms ceiling line and floor line are used for the lines where the wall meets the ceiling and the floor, respectively. For example, the terms are used in the book Architectural Drafting for Interior Designers (by Lydia Sloan Cline):

To make it more clear, I drew this diagram in Paint:

You can use the term cove or coving for the concave arched molding at the junction of a wall with a ceiling.

The definition of coving from britannica.com:

Coving, in architecture, concave molding or arched section of wall surface. An example is the curved soffit connecting the top of an exterior wall to a projecting eave. The curve typically describes a quarter-circle. The arched sections of a curved ceiling would be coving. Such a coved ceiling serves to join the vertical walls with a flat ceiling.

The definition of cove from Architect's Illustrated Pocket Dictionary (by Nikolas Davies, Erkki Jokiniemi):

1 a curved underside or soffit

2 coving; a concave moulding of plaster, timber or plastics, fixed as a decorative covering at the meeting of ceiling and wall; any meeting of ceiling and wall treated in this way; a cove tile; see also cavetto.

Note: In North America, the term crown molding is used for the molding at the junction of an interior wall and ceiling.

Answer 2

The cornice area is where walls and ceilings join.

From Home Design Directory

Answer 3

I'm a plasterer; it's called the arris (a junction where two flat surfaces meet).

arris
noun
ar·​ris | \ ˈa-rəs, ˈer-əs\
plural arris or arrises

the sharp edge or salient angle formed by the meeting of two surfaces especially in moldings

[Source: Merriam-Webster Dictionary]

And a more detailed explanation:

In architecture, an arris is the sharp edge formed by the intersection of two surfaces, such as the corner of a masonry unit; the edge of a timber in timber framing; the junction between two planes of plaster or any intersection of divergent architectural details. Also the raised edges which separate the flutings in a Doric column.

[Source: Wikipedia]