clearance n.

mid-14c., "make clear (an obscure subject) in the mind, explain, elucidate;" late 14c., "make clean, cleanse, purify; clarify (a liquid), remove what clouds or diminishes brightness or transparency;" also "prove innocent, vindicate;" of the weather, sea, sky, clouds, etc., "clear up, become fair or calm;" from clear (adj.).  Related: Cleared; clearing.

Intransitive sense of "become free from murkiness" is from 1580s. Meaning "to free from obstructions" is from 1520s; that of "to free from entanglement" is from 1590s; that of "pass (an obstacle) without entanglement or collision" is from 1630s. Sense of "to remove (something) out of the way" is from 1670s; that of "to clear land of trees and underbrush" is from 1690s. Meaning "to leap clear over" is first attested 1791. Meaning "to gain (a sum of money) in clear profit" is from 1719. Meaning "get approval for (a proposal, etc.) from authority" is from 1944; meaning "establish as suitable for national security work" is from 1948.

To clear (one's) throat is from 1881; earlier clear (one's) voice (1701). To clear out "depart, leave" (1825), perhaps is from the notion of ships satisfying customs, harbor regulations, etc., then setting sail. To get clear of is from 1590s. To clear up is from 1620s of weather, 1690s as "make clear to the mind." Clear the deck (1802) is from sailing ships. Clear the air in the figurative sense is from late 14c. To clear the coast (1520s) was to make it suitable for landing.

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.