The crossword solution for the term ANGLE START is TRI, which is a THREE-letter word. TRI is a Greek root word meaning 'THREE' and is used in many words to refer to something having THREE sides or angles. In geometry, an angle is a figure formed by two rays, or lines, that share a common endpoint. A triangle is a THREE-sided polygon, and the angles of a triangle add up to 180 degrees. Therefore, the crossword solution for ANGLE START is TRI, referring to the THREE angles of a triangle.