The most common and most likely answer to this crossword clue is the 7 letter word TERRENE
I've seen this crossword clue in The Guardian
T
E
R
R
E
N
E
More clues leading to the result TERRENE
Buddy explains!

The straight part
We know that "Mundane" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mundane = terrene.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 TERRENE mean?
TERRENE noun- The Earth's surface; the earth; the ground.
- Pertaining to the earth; earthly, terrestrial, worldly, as opposed to heavenly, marine.
- A broad, deep serving dish used for serving soup or stew.