c. 1300, "to estimate (number or size), calculate, count" (senses now obsolete), from Old French aesmer, esmer (Old North French amer) "to value, rate; count, estimate," ultimately from Latin aestimare "appraise, determine the value of" (see esteem (v.)).
Meaning in English apparently developed from "calculate," to "calculate with a view to action, plan," then to "direct a missile, a blow, etc." (late 14c.). Also used in Middle English of directing a letter, planting an altar, pitching a tent. Intransitive sense "intend, attempt" (early 14c.) was used by Shakespeare but is now considered colloquial. Related: Aimed; aiming.
late 14c., "a purpose, thing intended;" from aim (v.) or from nouns from the verb in Old French. Meaning "action of aiming" is from early 15c. To take aim originally was make aim (early 15c.).