The most common and most likely answer to this crossword clue is the 5 letter word MOUND
I've seen this crossword clue in The Guardian
M
O
U
N
D
More clues leading to the result MOUND
- Pile of money, money, money — small amount dropped off
- Large hill finally converted to small one
- Forces department to import blue berets in barrow, say
- First sixteen hours of the week storing uranium in pile
- Horse loses tail down hill
- Removed rib wasting away in an anthill
- Pitcher's location in the store
- Approaching death, after losing rib to pile of dirt
Buddy explains!

The straight part
We know that "small one" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case small one = mound.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 MOUND mean?
MOUND noun- An artificial hill or elevation of earth; a raised bank; an embankment thrown up for defense
- A natural elevation appearing as if thrown up artificially; a regular and isolated hill, hillock, or knoll.
- Elevated area of dirt upon which the pitcher stands to pitch.
- A ball or globe forming part of the regalia of an emperor or other sovereign. It is encircled with bands, enriched with precious stones, and surmounted with a cross.
- The mons veneris.
- (measurement) A hand.
- A protection; restraint; curb.
- A helmet.
- Might; size.
- To fortify with a mound; add a barrier, rampart, etc. to.
- To force or pile into a mound or mounds.