dependance (n.)

early 15c., dependaunce, "consequence, result, relation of a conclusion to a premise or an effect to a cause," from Old French dépendance (from dependre; see depend) and from Medieval Latin dependentia. Originally also dependance (which is the older of the two modern spellings), depending whether the writer had French or Latin foremost in mind; the Latin form gradually predominated, and after c. 1800 the spelling dependance is rare. For discussion, see dependant (n.).

From mid-15c. as "state of deriving existence, support, or direction from another." From 1620s as "reliance, confidence, trust." Literal meaning "fact of hanging from something" (1690s) was rare and is obsolete.

word-forming element attached to verbs to form abstract nouns of process or fact (convergence from converge), or of state or quality (absence from absent); ultimately from Latin -antia and -entia, which depended on the vowel in the stem word, from PIE *-nt-, adjectival suffix.

Latin present-participle endings for verbs stems in -a- were distinguished from those in -i- and -e-. Hence Modern English protestant, opponent, obedient from Latin protestare, opponere, obedire.

As Old French evolved from Latin, these were leveled to -ance, but later French borrowings from Latin (some of them subsequently passed to English) used the appropriate Latin form of the ending, as did words borrowed by English directly from Latin (diligence,absence).

English thus inherited a confused mass of words from French (crescent/croissant), and further confused it since c. 1500 by restoring -ence selectively in some forms of these words to conform with Latin. Thus dependant, but independence, etc.