monotone

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

• noun A succession of sounds or words uttered in a single tone of voice.
• noun A single tone repeated with different words or time values, especially in a rendering of a liturgical text.
• noun A chant in a single tone.
• noun Sameness or dull repetition in sound, style, manner, or color.
• adjective Characterized by or uttered in a monotone.
• adjective Of or having a single color.
• adjective Mathematics Designating sequences, the successive members of which either consistently increase or decrease but do not oscillate in relative value. Each member of a monotone increasing sequence is greater than or equal to the preceding member; each member of a monotone decreasing sequence is less than or equal to the preceding member.

from The Century Dictionary.

• To recite in a single, unvaried tone; intone; chant.
• noun A single or uniform tint or color.
• noun In rhetoric, a sameness of tone; the utterance of successive syllables at one unvaried pitch, with little or no inflection or cadence.
• noun Monotony or sameness of style in writing or speaking.
• noun In music:
• noun A single tone, without harmony or variation in pitch.
• noun Recitation of words in such a tone, especially in a church service, sometimes with harmonic accompaniment and with occasional inflections or melodic variations; intoning; chanting.
• noun Something spoken or written in one tone or strain.

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

• noun (Mus.) A single unvaried tone or sound.
• noun (Rhet.) The utterance of successive syllables, words, or sentences, on one unvaried key or line of pitch.

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

• adjective of speech or a sound having a single unvaried pitch
• adjective mathematics property of a function to be either always decreasing or always increasing
• noun A single unvaried tone of speech or a sound
• verb transitive, intransitive To speak in a monotone.

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

• adjective of a sequence or function; consistently increasing and never decreasing or consistently decreasing and never increasing in value
• adjective sounded or spoken in a tone unvarying in pitch
• noun an unchanging intonation
• noun a single tone repeated with different words or different rhythms (especially in rendering liturgical texts)