1620s, see tangent (adj.) + -ial. Figurative sense of "divergent, erratic" is from 1787; that of "slightly connected" is from 1825. Related: Tangentially.
Entries linking to tangential
tangent adj.
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.
-ial
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.