only

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

• adjective Alone in kind or class; sole.
• adjective Having no siblings.
• adjective Most suitable of all; superior or excellent.
• adverb Without anyone or anything else; alone.
• adverb At the very least.
• adverb And nothing else or more; merely; just.
• adverb Exclusively; solely.
• adverb In the last analysis or final outcome; inevitably.
• adverb With the negative or unfortunate result.
• adverb As recently as.
• adverb In the immediate past.
• conjunction Were it not that; except that.
• conjunction With the restriction that; but.
• conjunction However; and yet.

from The Century Dictionary.

• Single as regards number, or as regards class or kind; one and no more or other; single; sole: as, he was the only person present; the only answer possible; an only son; my only friend; the only assignable reason.
• Alone; nothing or nobody but.
• Mere; simple.
• Single in degree or excellence; hence, distinguished above or beyond all others; special.
• Alone; no other or others than; nothing or nobody else than; nothing or nobody but; merely: as, only one remained; man cannot live on bread only.
• No more than; merely; simply; just: as, he had sold only two.
• In but one manner, for but one purpose, by but one means, with but one result, etc.; in no other manner, respect, place, direction, circumstances, or condition than; at no other time, or in no other way, etc., than; for no other purpose or with no other result than; solely; exclusively; entirely; altogether: as, he ventured forth only at night; he was saved only by the skin of his teeth; he escaped the gallows only to be drowned; articles sold only in packages.
• Above all others; preëminently; especially.
• Singly; with no other in the same relation: as, the only begotten Son of the Father.
• Synonyms 1-3. Alone, Only. See alone.
• But; except; excepting that.
• Except; with the exception of.

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

• conjunction Save or except (that); -- an adversative used elliptically with or without that, and properly introducing a single fact or consideration.
• adjective One alone; single
• adjective Alone in its class; by itself; not associated with others of the same class or kind.
• adjective Alone, by reason of superiority; preëminent; chief.
• adverb In one manner or degree; for one purpose alone; simply; merely; barely.
• adverb So and no otherwise; no other than; exclusively; solely; wholly.
• adverb Singly; without more.
• adverb obsolete Above all others; particularly.

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

• adjective Alone in a category.
• adjective Singularly superior; the best.
• adjective Without sibling; without a sibling of the same gender.
• adjective obsolete Mere.
• adverb without others or anything further; exclusively
• adverb no more than; just
• adverb as recently as
• conjunction Under the condition that; but.
• conjunction However.
• conjunction But for the fact that; except.

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

• adverb in the final outcome