The most common and most likely answer to this crossword clue is the 7 letter word HUMDRUM
I've seen this crossword clue in The Guardian
H
U
M
D
R
U
M
More clues leading to the result HUMDRUM
- To sing with percussion accompaniment is boring
- Smell odd after day without incident
- Dull rhyming couplet — that’s one word for it
- Pal discarding clubs and diamonds? Odd routine
- Dull tone largely set by company executive before drink
- Boring hospital doctor beset by signs of indecision
- Boring noise that comes with percussion instrument
- Monotonous way to vocalise with instrument
- Dull thing that might accompany song and instrument
- Monotonous inarticulate murmur — dead strange
Buddy explains!

The straight part
We know that "Dull" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dull = humdrum.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HUMDRUM mean?
HUMDRUM noun- The quality of lacking variety or excitement.
- A stupid fellow.
- Lacking variety or excitement; dull; boring.