The most common and most likely answer to this crossword clue is the 4 letter word GRIT
I've seen this crossword clue in The Guardian
G
R
I
T
More clues leading to the result GRIT
- Guzzler emptied wine bottle
- Pluck guitar, instrument with nothing inside
- Good reputation involving toughness initially?
- Strength of character shown in Educating Rita
- Sand in bottle
- Indomitability? In short English monarch has it
- Abrasive particles in backbone
- Resolution, coarse stuff
- Courage that’s needed to deal with winter conditions?
- Good service ultimately lacking in stamina
Buddy explains!

The straight part
We know that "Sand/bottle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sand/bottle = grit.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 GRIT mean?
GRIT noun- A collection of hard small materials, such as dirt, ground stone, debris from sandblasting or other such grinding, or swarf from metalworking.
- Inedible particles in food.
- A measure of the relative coarseness of an abrasive material such as sandpaper, the smaller the number the coarser the abrasive.
- A hard, coarse-grained siliceous sandstone; gritstone. Also, a finer sharp-grained sandstone, e.g., grindstone grit.
- Strength of mind; great courage or fearlessness; fortitude.
- Apparently only in grit one's teeth: to clench, particularly in reaction to pain or anger.
- To cover with grit.
- To give forth a grating sound, like sand under the feet; to grate; to grind.
- (usually in the plural) Husked but unground oats.
- (usually in the plural) Coarsely ground corn or hominy used as porridge.