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The word is heptagon. A heptagon has 7 sides and 7 corners. If you join corners by straight lines from one corner to another corner you will find 5 triangles, but if you join all corners to a point in the centre you will find 7 triangles. The Heptathlon in athletics is a contest in which the participants must compete in 7 different athletic forms of athletics.
A nine sided shape has 7 triangles
9-2 = 7 triangles
7
If only 7 are colinear, then the question implies the lines need not go through every point. In that case there is an infinity of lines for each point.