The most common and most likely answer to this crossword clue is the 9 letter word EARTHWORM
I've seen this crossword clue in The Guardian
E
A
R
T
H
W
O
R
M
More clues leading to the result EARTHWORM
- Ticklish case in infectious air? One going underground
- Cook or warm the fisherman’s bait?
- Pink thing getting warmer, hot after a thrashing
- Thrower – man mostly recollected as gardener’s friend
- Tunneller finds planet getting hot — Arctic cap’s close to zero
- The war room could supply tunneller with nothing to spare
- Creepy-crawly ruining the marrow
- Spineless creature harassed war hero clutching last of retirement money
- Creature is warm; hotter when exposed timelessly
- Burrowing creature met harrow, sadly
Buddy explains!
The straight part
We know that "One going underground" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one going underground = earthworm.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 EARTHWORM mean?
EARTHWORM noun- A worm that lives in the ground.
- A worm of the family Lumbricidae, or, more generally, of the suborder Lumbricina.
- A contemptible person; a groveller.