At the end of §81, you were told that Latin 1st conjugation present participle derivatives should appear in English as words in -ant , -ance, and -ancy, and all the others as words in -ent, -ence, and -ency. That is true in theory, and it is usually true in practice (as we’ve just seen in §83). Unfortunately, the rule is slightly muddled by the influence of French, where all present participles are spelled in -ant. This means that there are some words in English that were transmitted through French with an -ant spelling, where one might expect an -ent. Only about a dozen Latin verbs were affected, but their derivatives can be tricky to spell correctly, especially for someone who knows Latin and is determined to follow the rule. In several bewildering cases, the same Latin verb has some English derivatives in -ant and others in -ent.
The verb pendere (“hang”) will illustrate this situation. Given the -ere of the present infinitive, we would expect derivatives in -ent; sure enough, the English ADJECTIVES pendent, dependent, and independent (“not hanging down from someone”) are spelled with an e, as are dependence, dependency, (both < L dependentia) and independence. However, the NOUN that means “a hanging ornament” is spelled pendant, and has a doublet pennant. Here is the French influence; if you find it confusing, you’re in good company. To their credit, the tax collectors at Revenue Canada know that the noun dependant is spelled with an a, even though the adjective dependent has an e.
In §82, we saw a number of tenere derivatives in -ent and -ence, as one would expect. However, tenant and tenancy show the French influence, as do maintenance (“holding in the hand”), lieutenant, and lieutenancy. The Anglo-Latin phrase locum tenens (used by doctors for a substitute “holding the place”) is precisely equivalent to lieutenant; it has a noun form locum-tenency that parallels lieutenancy.
English has two homonyms spelled mordant and mordent. Both come from the present participle of mordere (“bite”), and have the same etymological meaning “biting.” If wit is “biting,” it is mordant, but the musical embellishment is a mordent (via Italian). You can take your pick of ambiance or ambience (< L ambire), but the first should be spoken with a French accent. In the case of Renaissance and renascence (both “rebirth”), the first denotes a particular period in European history, and the second can be any resurgence.
Other spelling quirks include derivatives of tendere (attendant and attendance, as opposed to superintendent and tendency); defendere (defendant); dormire, “sleep” (dormant, dormancy); servire (servant, but subservient); scandere, “climb” (ascendant, descendant, but transcendent); sistere, “stand” (assistant, assistance, resistant, resistance alongside consistent, existence, insistent, persistent, subsistence). There’s inconsistency for you!