interior angle

1 3.9

The space inside a shape with straight sides where two sides meet

noun
/ɪnˈtɪriər ˈæŋɡəl/

Specialized

: ángulo interior

So since I have a pair of alternate interior angles that are the same measure, what that tells me is these two lines are parallel.

Examples

Then what we last talked about was what is what about the measure of one interior angle when your Polygon is regular?
Basic axioms: Sigma interior angles = 180 degrees.

Academic text (1998)
The interior angle of a triangle is always smaller than 180 degrees.
In a quadrilateral, the sum of the interior angles is 360 degrees.
Each interior angle of a regular pentagon measures 108 degrees.

Synonyms

internal angle

vsinterior angle

Specialized

4.2

The angle inside a polygon where two sides meet

is identical in meaning but uses alternative wording

How Large

reflex angle

Specialized

5.8

obtuse angle

Specialized

1 3.4

interior angle

Specialized

1 3.9

acute angle

Specialized

1 2.8

Surface Forms

interior angle singular

interior angles plural

Morphology

interior + angle

The meaning 'an angle formed inside a polygon by two adjacent sides' is directly and transparently derived from combining 'interior' (inside) with 'angle' (the geometric measure between two lines). This compositional noun phrase follows standard English and cross-linguistic patterns, so a B1 learner who knows both constituents would readily understand it.

Etymology

Interior angle shows a simple picture: interior means 'inside' and angle is the corner where two sides meet, so an interior angle is the corner 'inside' a shape with straight sides.