Monotonous means boringly unchanging. A monotonous voice, monotonous work, monotonous and grey.
The complaint is sameness rather than difficulty — monotonous work may be easy and still be unbearable, which is why job design pays so much attention to variety. The word is Greek: one tone, from a voice that never changes pitch, and that is the oldest and most literal use.
1adjectivemonotonousBoringly unchanging.
“Working on the assembly line was monotonous; he did the same task all day.”
synonyms: repetitive, tedious
monotonous is a quality of sameness.
Latin
monotonus — unvarying in tone
English
monotone
English, today
monotonous
Built from
From monotone + -ous. monotone comes from the post-Classical Latin monotonus (“unvarying in tone”) or its etymon the Ancient Greek - μονότονος (“steady”, “unwavering”); compare cognate adjectives, namely the French monotone, the German monoton, the Italian monotono, and the Spanish monótono, as well as the slightly earlier English noun monotony and adjective monotonical.
Etymology from Wiktionary, CC BY-SA