The most common and most likely answer to this crossword clue is the 6 letter word SNEEZE
I've seen this crossword clue in The Guardian
S
N
E
E
Z
E
More clues leading to the result SNEEZE
- Quick expulsion of unknown European, first seen at sea
- Beginning to sense joints, reportedly a symptom of flu
- Outburst unfortunately seen by disheartened Zeke?
- Start to smoke joints audibly, showing sign of irritation
- Rapid blast from hooter
- Sun on knees, they say, causes symptom of a cold
- 19 Southwestern enterprise zone vacated in allergic response
- Suddenly stop Poles hiding French evidence of disease
- Small joints allegedly lead to explosion
- Partners and opponent, three times holding unknown hand, might catch this?
Buddy explains!

The straight part
We know that "Outburst" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case outburst = sneeze.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 SNEEZE mean?
SNEEZE noun- An act of sneezing.
- To expel air as a reflex induced by an irritation in the nose.
- To expel air as if the nose were irritated.