pivotal (adj.)

"pin on which a wheel or other object turns," 1610s, from French pivot, from Old French pivot "hinge pin, pivot" (12c.), also "penis," a word of uncertain origin. Pevetsheres, evidently some kind of shears, is mentioned in a will registered in York in 1398. Figurative sense of "turning point, that on which some matter hinges or depends" is recorded from 1813.

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)).