drone

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

• noun A male bee, especially a honeybee, that is characteristically stingless, performs no work, and produces no honey. Its only function is to mate with the queen bee.
• noun An idle person who lives off others; a loafer.
• noun A person who does tedious or menial work; a drudge.
• noun A pilotless aircraft operated by remote control.
• intransitive verb To make a continuous low dull humming sound.
• intransitive verb To speak in a monotonous tone.
• intransitive verb To pass or act in a monotonous way.
• intransitive verb To utter in a monotonous low tone.
• noun A continuous low humming or buzzing sound.
• noun Any of the pipes of a bagpipe that lack finger holes and produce a single tone.
• noun A long sustained tone.
• noun Any of various instruments that produce only a constant pitch.

from The Century Dictionary.

• To roar; bellow.
• To give forth a monotonous, unvaried tone; utter a dull humming sound; hum or buzz, as a beetle or a bagpipe.
• To use a dull, monotonous tone: as, he drones in his reading.
• To give forth or utter in a monotonous, dull tone: as, he drones his sentences.
• To live in idleness.
• noun The male of the honey-bee.
• noun Hence An idler; a sluggard; one who lives on the labor of others.
• noun A monotonous, continued tone or sound; a humming: as, the drone of a bee.
• noun In music: A pipe in the bagpipe which gives out a continuous and invariable tone.
• noun A drone-bass.
• noun The tone emitted by the drone of a bagpipe.

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

• intransitive verb To utter or make a low, dull, monotonous, humming or murmuring sound.
• intransitive verb To love in idleness; to do nothing.
• noun (Zoöl.) The male of bees, esp. of the honeybee. It gathers no honey. See honeybee.
• noun One who lives on the labors of others; a lazy, idle fellow; a sluggard.
• noun That which gives out a grave or monotonous tone or dull sound; as: (a) A drum. [Obs.] Halliwell. (b) The part of the bagpipe containing the two lowest tubes, which always sound the key note and the fifth.
• noun A humming or deep murmuring sound.
• noun (Mus.) A monotonous bass, as in a pastoral composition.

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

• noun A male bee or wasp, which does not work but can fertilise the queen (Wikipedia).
• noun Someone who doesn't work; a lazy person, an idler.
• noun A remotely controlled aircraft, an unmanned aerial vehicle (UAV, Wikipedia).
• verb To produce a low-pitched hum or buzz.
• verb To speak in a monotone way.
• noun A low-pitched hum or buzz.
• noun One who performs menial or tedious work; a drudge.
• noun One of the fixed-pitch pipes on a bagpipe.
• noun A genre of music similar to that of noise.

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

• noun stingless male bee in a colony of social bees (especially honeybees) whose sole function is to mate with the queen
• noun a pipe of the bagpipe that is tuned to produce a single continuous tone
• verb talk in a monotonous voice
• noun someone who takes more time than necessary; someone who lags behind
• verb make a monotonous low dull sound
• noun an unchanging intonation
• noun an aircraft without a pilot that is operated by remote control