apt

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Exactly suitable; appropriate.
• adjective Having a natural tendency; inclined.
• adjective Quick to learn or understand.

from The Century Dictionary.

• To prepare for a definite service; fit; suit for anticipated circumstances; adapt.
• Possessing the qualities necessary or proper for a certain purpose or end; fit; suited; adapted; suitable.
• Suited to its purpose; apposite; pertinent; appropriate; becoming: as, an apt metaphor.
• Having a tendency; naturally susceptible; liable; likely: as, wheat on moist land is apt to blast or be winter-killed.
• Inclined; predisposed; disposed customarily; prone; ready: as, one who is too apt to slander others.
• Ready; prompt; quick; unusually intelligent; expert; facile: as, a pupil apt to learn; an apt wit.
• Prepared; ready; willing.
• Capable of easy explanation; natural; credible.
• Synonyms Apt, Fit. “The words apt and fit might be thought to differ only in this, that the former is of Latin derivation; but apt has an active sense, and fit a passive sense,—a distinction clearly shown by Shakspere, when the poisoner in the play in Hamlet says, ‘hands apt, drugs fit,’ and by Wordsworth: ‘Our hearts more apt to sympathize with heaven, our souls more fit for future glory.’” H. Reed, Eng. Lit., p. 106. Meet, fitting, germane, appropriate.3 and . Apt, Likely, Liable, Subject, prone. Apt, when used in this sense of persons, indicates physical tendency or inward inclination: as, apt to catch cold; apt to neglect work; when used of things, it similarly indicates natural tendency: as, apt to mold. Likely may suggest the same idea: as, he is likely to do it; it is likely to rust; or it may express mere external probability or chance: as, he is likely to come at any moment. Liable in this connection is properly used only of exposure to evil, being practically equivalent to exposed, or exposed to the danger of: as, liable to accident; liable to be hurt, that is, exposed to the danger of being hurt; liable to censure: in such use it does not express probability or tendency, but merely the possibility of exposure or risk. Subject expresses what is likely to happen to a person or thing, and occasionally does happen. Liable to disease and subject to disease thus convey different ideas. The things to which we are liable are determined more by accident or circumstance; the things to which we are subject are determined by nature and constitution. Apt to be suddenly ill; liable, but not likely, to die before the physician arrives; subject to attacks of epilepsy.
• Clever, bright, dexterous.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb obsolete To fit; to suit; to adapt.
• adjective Fit or fitted; suited; suitable; appropriate.
• adjective Having an habitual tendency; habitually liable or likely; -- used of things.
• adjective Inclined; disposed customarily; given; ready; -- used of persons.
• adjective Ready; especially fitted or qualified (to do something); quick to learn; prompt; expert

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Suitable; appropriate; fit or fitted; suited.
• adjective of persons or things Having a habitual tendency; habitually liable or likely; disposed towards.
• adjective Ready; especially fitted or qualified (to do something); quick to learn; prompt; expert; as, a pupil apt to learn; an apt scholar.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective (usually followed by `to') naturally disposed toward
• adjective being of striking appropriateness and pertinence
• adjective at risk of or subject to experiencing something usually unpleasant
• adjective mentally quick and resourceful