The word 'tangential' originates from the Latin verb tangere, meaning 'to touch'. This root gave rise to the mathematical term 'tangent', describing a line that merely touches a curve without intersecting it. The adjectival suffix '-ial' was added to form 'tangential', literally meaning 'of or relating to a tangent'. The modern figurative sense, meaning 'only slightly connected' or 'peripheral', derives logically from this geometric concept: just as a tangent only makes brief, superficial contact with a curve, a tangential remark only touches on the main subject in a passing, indirect manner.

Structure: tangent (touching line) + ial (adjective suffix) - tangent: From Latin tangent- (stem of tangens), present participle of tangere (to touch). In mathematics, a line that touches a curve at a single point. - ial: A suffix forming adjectives, from Latin -ialis, indicating 'relating to or characterized by'.