1590s, "meeting at a point without intersecting," from Latin tangentem (nominative tangens), present participle of tangere "to touch," from PIE root *tag- "to touch, handle." First used by Danish mathematician Thomas Fincke in "Geomietria Rotundi" (1583). Extended sense of "slightly connected with a subject" is first recorded 1825. Related: Tangence; tangency.
adjectival word-forming element, variant of -al (1) with connective -i-. From Latin -ialis, in which the -i- originally was from the stem of the word being attached but later came to be felt as connective.
Others are reading
<a href="https://www.etymonline.com/word/tangential">Etymology of tangential by etymonline</a>
Harper, D. (n.d.). Etymology of tangential. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/tangential