twelfth

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

• noun The ordinal number matching the number 12 in a series.
• noun One of 12 equal parts.

from The Century Dictionary.

• Next in order after the eleventh: an ordinal numeral.
• Being one of twelve equal parts into which a whole is regarded as divided.
• noun One of twelve equal parts of anything; the quotient of unity divided by twelve.
• noun In early English law, a twelfth of the rents of the year, or of movables, or both, granted or levied by way of tax.
• noun In music, a tone twelve diatonic degrees above or below a given tone, or the interval between two such tones; a compound fifth.
• noun In organ-building, a stop giving tones a twelfth above the normal pitch of the digitals used.
• noun Twelfth-day.

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

• adjective Next in order after the eleventh; coming after eleven others; -- the ordinal of twelve.
• adjective Constituting, or being one of, twelve equal parts into which anything is divided.
• noun The quotient of a unit divided by twelve; one of twelve equal parts of one whole.
• noun The next in order after the eleventh.
• noun (Mus.) An interval comprising an octave and a fifth.

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

• adjective ordinal The ordinal form of the number twelve, describing a person or thing in position number 12 of a sequence.
• noun fractional One of twelve equal parts of a whole.
• noun music An interval equal to an octave plus a fifth

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

• adjective coming next after the eleventh and just before the thirteenth in position
• noun one part in twelve equal parts
• noun position 12 in a countable series of things