The most common and most likely answer to this crossword clue is the 10 letter word STALAGMITE
I've seen this crossword clue in The Daily Telegraph
S
T
A
L
A
G
M
I
T
E
More clues leading to the result STALAGMITE
- At war camp, little child that grows up
- One seen in cave is a little bit camp, at first
- The point of growing long-term deposits?
- POW camp force, we hear, is rising in cave
- One growing up as prison child
- Pillar of the underground in prison having served time
- Get atlas out crossing motorway, seeing pillar pointing up
- POW camp has small arachnid and limestone deposit
- Street party upset by a small bug on a cave structure
- POW camp item changed rock formation
Buddy explains!
The straight part
We know that "Pillar of the underground" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pillar of the underground = stalagmite.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 STALAGMITE mean?
STALAGMITE noun- A secondary mineral deposit of calcium carbonate or other mineral, in shapes similar to icicles, that lie on the ground of a cave.