Geometry language crossword vocabulary pack

Teacher key

1. TRIANGLE · 8 letters · noun · introductory
   Polygon with three sides

   Hint: Its interior angles add to 180 degrees in Euclidean geometry.
   Why it fits: TRIANGLE fits because three straight sides enclose this basic polygon used throughout geometry.

2. QUADRILATERAL · 13 letters · noun · intermediate
   Polygon with four sides

   Hint: Squares, rectangles, and trapezoids are examples.
   Why it fits: QUADRILATERAL is correct because all four-sided polygons belong to this broad geometry class.

3. POLYGON · 7 letters · noun · introductory
   Closed plane figure made of straight segments

   Hint: Circles do not qualify because their edge is curved.
   Why it fits: POLYGON fits because triangles, rectangles, and pentagons are all closed figures with straight sides.

4. VERTEX · 6 letters · noun · introductory
   Corner point where sides or edges meet

   Hint: A square has four of these points.
   Why it fits: VERTEX is correct because angles, polygons, and solids all use this word for a corner or endpoint meeting place.

5. RADIUS · 6 letters · noun · introductory
   Segment from a circle's center to its edge

   Hint: It is half the diameter.
   Why it fits: RADIUS fits because every point on a circle is the same distance from the center by this measure.

6. DIAMETER · 8 letters · noun · introductory
   Circle segment through the center with endpoints on the edge

   Hint: It equals two radii.
   Why it fits: DIAMETER is correct because it is the longest chord of a circle and measures twice the radius.

7. CIRCUMFERENCE · 13 letters · noun · intermediate
   Distance around a circle

   Hint: It is calculated with pi and the diameter.
   Why it fits: CIRCUMFERENCE fits because it measures the complete boundary length of a circle.

8. CHORD · 5 letters · noun · intermediate
   Segment with both endpoints on a circle

   Hint: The longest one passes through the center.
   Why it fits: CHORD is correct because it connects two points on the circle, whether or not it crosses the center.

9. TANGENT · 7 letters · noun · intermediate
   Line that touches a circle at exactly one point

   Hint: At the touch point, it is perpendicular to a radius.
   Why it fits: TANGENT fits because it just touches the circle rather than cutting through it.

10. SECANT · 6 letters · noun · advanced
    Line that intersects a circle at two points

    Hint: Unlike a touching-only line, it cuts across the circle.
    Why it fits: SECANT is correct because it passes through the circle and contains a chord between the two intersections.

11. ARC · 3 letters · noun · introductory
    Curved part of a circle's edge

    Hint: It lies between two points on the circle.
    Why it fits: ARC fits because it is not the whole circle, only a curved section along the circumference.

12. CONGRUENT · 9 letters · adjective · intermediate
    Having the same size and shape

    Hint: One figure could be moved onto the other exactly.
    Why it fits: CONGRUENT fits because translations, rotations, and reflections can place matching figures directly on top of each other.

13. SIMILAR · 7 letters · adjective · intermediate
    Having the same shape but possibly different size

    Hint: Corresponding angles match, and side lengths are proportional.
    Why it fits: SIMILAR is correct because one figure can be a scaled version of the other without being the same size.

14. SYMMETRY · 8 letters · noun · introductory
    Balanced property with matching parts

    Hint: A folded shape may have two halves that line up.
    Why it fits: SYMMETRY fits because a shape may remain aligned with itself after a flip, turn, or other transformation.

15. ROTATION · 8 letters · noun · introductory
    Transformation that turns a figure around a point

    Hint: The amount may be measured in degrees.
    Why it fits: ROTATION fits because each point moves along a circular path around the center while size and shape stay unchanged.

16. REFLECTION · 10 letters · noun · introductory
    Transformation that flips a figure over a line

    Hint: Mirror images across an axis show this motion.
    Why it fits: REFLECTION is correct because points move to equal distances on the opposite side of the mirror line.

17. TRANSLATION · 11 letters · noun · introductory
    Transformation that slides a figure without turning

    Hint: Every point moves the same distance in the same direction.
    Why it fits: TRANSLATION fits because the figure's size, shape, and orientation stay the same while its position changes.

18. DILATION · 8 letters · noun · intermediate
    Transformation that enlarges or reduces a figure

    Hint: A scale factor controls the new size.
    Why it fits: DILATION is correct because it creates a similar figure by multiplying distances from a center by the same factor.

19. BISECTOR · 8 letters · noun · intermediate
    Line or ray that divides something into two equal parts

    Hint: It can split an angle or segment evenly.
    Why it fits: BISECTOR fits because it names the divider that creates two congruent angles or two congruent segment pieces.

20. PARALLEL · 8 letters · adjective · introductory
    Describing coplanar lines that never meet

    Hint: They stay the same distance apart.
    Why it fits: PARALLEL is correct because these lines have the same direction and remain equidistant in Euclidean geometry.

Accept a different answer only when it matches the clue, length, grammar, and any supplied crossings. Use the reviewed answer when teaching the intended vocabulary target.