trapezoidal (adj.)

1706, "a trapezium," from Modern Latin trapezoides, from Late Greek trapezoeides, noun use by Euclid of Greek trapezoeides "trapezium-shaped," from trapeza, literally "table" (see trapezium), + -oeides "shaped" (see -oid). Technically, a plane four-sided figure with no two sides parallel. But in English since c. 1800, often confused with trapezium in its sense of "a quadrilateral figure having only sides parallel and two not."

suffix forming adjectives from nouns or other adjectives, "of, like, related to, pertaining to," Middle English -al, -el, from French or directly from Latin -alis (see -al (2)).