The most common and most likely answer to this crossword clue is the 4 letter word GALL
I've seen this crossword clue in The Guardian
G
A
L
L
More clues leading to the result GALL
- Bitterness of everyone after end of squabbling
- Outgrowth caused by parasite in cheek
- Work off fast run, being sore
- Bitterness caused by broadcast of Asterix, perhaps
- Dracula’s not quite last to linger over neck
- Bitterness when local girl has left
- Sauce is good on everything
- Girl left with hard feelings
- Bladder that may be removed for impertinence
- Lass having left — a source of irritation
Buddy explains!

The straight part
We know that "Outgrowth caused by parasite/cheek" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case outgrowth caused by parasite/cheek = gall.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 GALL mean?
GALL noun- Bile, especially that of an animal; the greenish, profoundly bitter-tasting fluid found in bile ducts and gall bladders, structures associated with the liver.
- The gall bladder.
- Great misery or physical suffering, likened to the bitterest-tasting of substances.
- A feeling of exasperation.
- Impudence or brazenness; temerity, chutzpah.
- A sore or open wound caused by chafing, which may become infected, as with a blister.
- A sore on a horse caused by an ill-fitted or ill-adjusted saddle; a saddle sore.
- A pit on a surface being cut caused by the friction between the two surfaces exceeding the bond of the material at a point.
- To bother or trouble.
- To harass, to harry, often with the intent to cause injury.
- To chafe, to rub or subject to friction; to create a sore on the skin.
- To exasperate.
- To cause pitting on a surface being cut from the friction between the two surfaces exceeding the bond of the material at a point.
- To scoff; to jeer.
- A blister or tumor-like growth found on the surface of plants, caused by burrowing of insect larvae into the living tissues, especially that of the common oak gall wasp Cynips quercusfolii.
- A bump-like imperfection resembling a gall.
- To impregnate with a decoction of gallnuts in dyeing.