Humdrum means dull through endless repetition. A humdrum job, humdrum routine, humdrum and grey.
The repetition is what makes it dull, which is a narrower charge than boring — a humdrum life is not empty, it is the same every day. The word sounds like what it means, and that is roughly what it is: a reduplication built on hum, the sound of monotony. Note that it works as adjective and noun.
1adjectivehumdrumDull through endless repetition.
“She wanted to escape her humdrum job at the bank and travel the world.”
synonyms: monotonous, dreary
humdrum is a quality of dullness.
possible a reduplication of hum, 1550s.
Etymology from Wiktionary, CC BY-SA