fluent

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

• adjective Able to express oneself readily and effortlessly.
• adjective Flowing effortlessly; polished.
• adjective Flowing or moving smoothly; graceful.
• adjective Flowing or capable of flowing; fluid.

from The Century Dictionary.

• Flowing or capable of flowing; having a flowing motion, or an appearance as of flowing; changeable; not rigid.
• Ready in the use of words; using words with facility; voluble: as, a fluent speaker or writer.
• Proceeding from a facility of ready copious speech; marked by copiousness of speech: as, fluent utterance; a fluent style.
• noun A stream; a current of water.
• noun In the doctrine of fluxions, the variable or flowing quantity in fluxions which is continually increasing or decreasing; an integral. See fluxion.
• In fluxions, enlarging (or diminishing) continuously, that is, by infinitesimal increments (+ or —).

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

• noun obsolete A current of water; a stream.
• noun (Math.) A variable quantity, considered as increasing or diminishing; -- called, in the modern calculus, the function or integral.
• adjective Flowing or capable of flowing; liquid; glodding; easily moving.
• adjective Ready in the use of words; voluble; copious; having words at command; and uttering them with facility and smoothness; ; hence, flowing; voluble; smooth; -- said of language.

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

• adjective That flows; flowing, liquid.
• adjective linguistics Able to speak a language accurately, rapidly, and confidently – in a flowing way.

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

• adjective smooth and unconstrained in movement
• adjective expressing yourself readily, clearly, effectively