Here are the two entries from Anthony Lo Bello's Origins of Mathematical Words (John Hopkins, 2013) which is very informative, entertaining, and perhaps curmudgeonly. In his parlance, following the lexicographer Samuel Johnson, a "low word" is one with an "irregular combination" of roots that has "little or no etymological legitimacy."
dynamical The Greek noun [dunamis] means power. The corresponding Greek adjective is [dunamikos], pertaining to power. The correct English adjective is therefore dynamic. To superimpose the vestige -al of the Latin adjectival ending -alis upon the stem of a Greek adjective is often the product of ignorance and produces a low word. In other cases, the addition of the Latin suffix to the Greek adjective is due to the fact that a different meaning is intended from that of the Greek adjective; thus, dynamic was an established word, so one spoke of dynamical systems rather than dynamic systems to avoid confusion.
tangential See the entry tangent. The Latin adjectival suffix -alis was added to the stem of the participle tangens, tangentis, which was already an adjective but felt to be a noun, the tangent.