The most common and most likely answer to this crossword clue is the 9 letter word GRENADIER
I've seen this crossword clue in The Guardian
G
R
E
N
A
D
I
E
R
More clues leading to the result GRENADIER
- Gardener I trained as specialist in pineapples?
- Head of garrison more disposed to accept new infantryman
- Angry gardener catches one loaded with pineapples once
- E’er daring, happily I pulled the pin on mine
- Dearer gin upset guard
- Soldier wants a bit of work on retirement, loved one said
- Soldier on with one European, going around south of Greece
- Soldier rereading novel
- Re-reading this word upset a soldier
- Dire anger could be what makes me a bomb-thrower
Buddy explains!

The straight part
We know that "a soldier" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a soldier = grenadier.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 GRENADIER mean?
GRENADIER noun- A type of soldier, originally one who threw grenades, later a member of a company formed from the tallest men of the regiment; now specifically, a member of the Grenadier Guards.
- Any of various African weaverbirds or waxbills, especially the common grenadier or the red bishop.
- Any of various deep-sea fish of the family Macrouridae that have a large head and body and a long tapering tail; a rattail.