WordNet sense 1 (someone who takes more time than necessary; someone who lags behind):

dawdler, laggard, poke, trailer, lagger

WordNet sense 2 (an unchanging intonation):

monotone, droning

WordNet sense 3 (an aircraft without a pilot that is operated by remote control):

pilotless aircraft, radio-controlled aircraft

WordNet sense 4 (a pipe of the bagpipe that is tuned to produce a single continuous tone):

bourdon, drone pipe

WordNet sense 5 (talk in a monotonous voice):

drone on