explain

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

• intransitive verb To make plain or comprehensible.
• intransitive verb To define; expound.
• intransitive verb To offer reasons for or a cause of; justify.
• intransitive verb To offer reasons for the actions, beliefs, or remarks of (oneself).
• intransitive verb To make something plain or comprehensible.

from The Century Dictionary.

• To make plain or flat; spread out in a flattened form; unfold.
• To make plain or clear to the mind; render intelligible; unfold, analyze, state, or describe in such a manner as to make evident to the minds of others; exhibit the nature, meaning, or significance of; interpret; elucidate; expound.
• To exhibit, disclose, or state the grounds or causes of the existence or occurrence of; reveal or state the causal or logical antecedents or conditions of; account for.
• Synonyms Explain, Expound, Interpret, Elucidate. Explain is the most general of these words, and means to make plain, clear, and intelligible. Expound is used of elaborate, formal, or methodical explanation: as, to expound a text, the law, the philosophy of Aristotle. To interpret is to explain, as if from a foreign language, to make clear what before was dark, and generally by following the original closely, as word by word and line by line: as, to interpret Hegel, Swedenborg, Emerson. To elucidate is to bring or work out into the light that which before was dark, usually by means of illustration; the word generally implies, like expound, a somewhat protracted or elaborate process. See translate.
• To give explanations.

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

• intransitive verb To give an explanation.
• transitive verb obsolete To flatten; to spread out; to unfold; to expand.
• transitive verb To make plain, manifest, or intelligible; to clear of obscurity; to expound; to unfold and illustrate the meaning of.
• transitive verb to get rid of by explanation.

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

• verb To give a sufficiently detailed report about (a) the reason for something, about why something happened, about a causal chain of events; about (b) how something works, about how elements in a system interact; about (c) how to do something, about the steps which need to be accomplished in order to accomplish a certain goal.
• verb To give a valid excuse for some past behavior.
• verb obsolete To make flat, smooth out.
• verb obsolete To unfold or make visible.

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

• verb serve as a reason or cause or justification of
• verb make plain and comprehensible
• verb define