monotony (n.)

• alliteration
• assonance
• boredom
• ceaselessness
• chime
• constancy
• continuity
• continuousness
• drone
• dryness
• endlessness
• ennui
• equilibrium
• flatness
• frequency
• fullness
• fundamental
• harmonic
• humdrum
• incessancy
• intonation
• invariability
• irk
• jingle
• monologue
• monotone
• orderliness
• overtone
• partial
• pitch
• pitter-patter
• plenitude
• regularity
• repetitiousness
• repetitiveness
• rhyme
• sameness
• singsong
• smoothness
• stability
• steadiness
• successiveness
• tedium
• tone
• treadmill
• trot
• uniformity