The most common and most likely answer to this crossword clue is the 8 letter word MIGRAINE
I've seen this crossword clue in The Guardian
M
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More clues leading to the result MIGRAINE
- Male that is eating corn, say, gets a headache
- Bad headache from one rye, perhaps, consumed by me
- Shimmering in image around retina's start - of one perhaps
- Headache as fighter plane almost came down
- Pain in the head teacher’s rear? Imagine rioting
- Condition of Russian fighter’s low grade after downpour
- Male that is gathering farm produce gets a headache
- Russian fighter fell down almost, due to medical condition
- The writer, swallowing one rye, say, getting headache
- Setter taking one small measure from apothecary for nasty headache
Buddy explains!

The straight part
We know that "Condition" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case condition = migraine.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 MIGRAINE mean?
MIGRAINE noun- A severe, disabling headache, usually affecting only one side of the head, and often accompanied by nausea, vomiting, photophobia and visual disturbances.
- A neurological condition characterised by such headaches.