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 of 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*.