Verb

Middle English amounten "to mount (a horse), increase, (of a sum, period of time) add up (to), come (to), be worth, be equal (to)," borrowed from Anglo-French amunter, amounter (continental Old French amonter) "to rise, increase, be worth, add up (to)," derivative of amunt, amount (continental Old French amont) "above, upward," univerbation of the adverbial phrase a mont "upward," literally "to the mountain," from a "to" (going back to Latin ad) + mont "mountain," going back to Latin mont-, mons — more at ad-, mount entry 1

Note: Alternatively Old French and Anglo-French amunter, amonter could be taken as a derivative of munter, monter "to mount" (see mount entry 2) with the prefix a-, usually forming transitive verbs. Französisches etymologisches Wörterbuch lists the verb under both the etymon mons and *montare.

Noun

Middle English amunte, borrowed from Anglo-French, noun derivative of amunter "to rise, increase, be worth, add up (to)" — more at amount entry 1

Note: The noun is sparsely attested in Middle English and Anglo-French, and the post-medieval English noun should probably be taken as directly derived from the verb amount entry 1.

Verb

14th century, in the meaning defined at sense 1a

Noun

15th century, in the meaning defined at sense 1a