Ill-considered break-out (4)
I believe the answer is:
rash
'ill-considered' is the definition.
(synonyms)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for rash that I've seen before include "Outbreak; hasty" , "sign of irritation?" , "Over-hasty, reckless" , "Impulsive - eruption" , "Impetuous; skin ailment" .)