The most common and most likely answer to this crossword clue is the 5 letter word SLIME
I've seen this crossword clue in The Times
S
L
I
M
E
More clues leading to the result SLIME
- It's wet and sticky topping of stewed fruit
- Gooey stuff coming from small tree
- Little son touching green filth
- Mother making version of muesli, not universal
- Gooey stuff, not fat, on rear of univalve
- One associated with detectives is, in short, returning oily servility
- French boy’s looking up meaning of “gunk”
- Son covers fruit tree’s ooze
- Bit of smelly green goo
- Filth from birds finally landing on tree
Buddy explains!

The straight part
We know that "Gooey stuff" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case gooey stuff = slime.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 SLIME mean?
SLIME noun- Soft, moist earth or clay, having an adhesive quality; viscous mud; any substance of a dirty nature, that is moist, soft, and adhesive; bitumen; mud containing metallic ore, obtained in the preparatory dressing.
- Any mucilaginous substance; or a mucus-like substance which exudes from the bodies of certain animals, such as snails or slugs.
- A sneaky, unethical person; a slimeball.
- A monster having the form of a slimy blob.
- Human flesh, seen disparagingly; mere human form.
- Jew’s slime (bitumen)
- Friend, homie
- To coat with slime.
- To besmirch or disparage.
- To carve (fish), removing the offal.