The most common and most likely answer to this crossword clue is the 5 letter word SOLID
I've seen this crossword clue in The Guardian
S
O
L
I
D
More clues leading to the result SOLID
- Firm one enters changed hands
- Humming after crossword essentially well-constructed
- Large raise to join top firm
- Fluid occasionally seen in ground that’s like rock?
- Small, smelly and dense
- Strong oils mixed by daughter
- Firm dealt in clothing items, primarily
- Sound thick
- PRISM, for example, is old scheme
- Sound from one getting pushed around
Buddy explains!

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 SOLID mean?
SOLID noun- A substance in the fundamental state of matter that retains its size and shape without need of a container (as opposed to a liquid or gas).
- A three-dimensional figure (as opposed to a surface, an area, or a curve).
- A favor.
- An article of clothing which is of a single color throughout.
- (in the plural) Food which is not liquid-based.
- (of an object or substance) That can be picked up or held, having a texture, and usually firm. Unlike a liquid or a gas.
- Large in size, quantity, or value.
- Lacking holes, hollows or admixtures of other materials.
- Strong or unyielding.
- Excellent, of high quality, or reliable.
- Hearty; filling.
- Worthy of credit, trust, or esteem; substantial; not frivolous or fallacious.
- Financially well off; wealthy.
- Sound; not weak.
- Written as one word, without spaces or hyphens.
- Not having the lines separated by leads; not open.
- United; without division; unanimous.
- Of a single color throughout.
- (of drawn lines) Continuous; unbroken; not dotted or dashed.
- Having all the geometrical dimensions; cubic.
- Solidly.
- Without spaces or hyphens.