triangle noun BrE /ˈtraɪæŋɡl/ ; NAmE /ˈtraɪæŋɡl/

a flat shape with three straight sides and three angles; a thing in the shape of a triangle

(British English) a right-angled triangle

(North American English) a right triangle

Cut the sandwiches into triangles.

triangular adjective BrE /traɪˈæŋɡjələ(r)/ ; NAmE /traɪˈæŋɡjələr/ ​ shaped like a triangle

This lady in the video seems to be a native speaker and she said "triangle to the triangle hole" (at 1:10). She said "circle to the circle hole ..." (at 1:20).

Why didn't she say "triangular hole"?

Similarly, "rectangle" (noun) -> rectangular (adj)

But "square" (noun); "oval" (noun) --> "square" (adjective); "oval" (adj)

But"circle" (noun) --> round (adj)

Why didn't she say "triangular hole" instead of "triangle hole" and "round hole" instead of "circle hole"?

  • 1
    She actually says, “Triangle - for the triangle hole.” This is perfectly idiomatic for the simplified way she is describing the toy and her actions. It is almost “baby speak” - she is deliberately simplifying her language and avoiding complex words like “triangular”. Jan 18, 2020 at 3:40

1 Answer 1


As Orbital Aussie noted, the speaker is using 'baby speak' to make it easier.

The correct term is:

triangular hole

Similarly, you have quoted a difference between British and North American English, whereas my experience of both places is that use of the term 'right-angled triangle' would be used when speaking formally and / or to adults, whereas you might hear the term 'right triangle' in, for example, a primary school with young children for whom the word 'angle' might represent a more abstract concept and impede their understanding.

Also, using the phrase 'right triangle' could lead to ambiguity, since you might mean the 'correct triangle' (which could be isosceles or scalene), rather than a right-angled triangle.

Hope that helps,


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