The most common and most likely answer to this crossword clue is the 7 letter word AILMENT
I've seen this crossword clue in The Times
A
I
L
M
E
N
T
More clues leading to the result AILMENT
- I lament needing treatment for illness
- Complaint the German’s missing problem with train
- Dreadful meal in time causes illness
- Sick inmate nursing ultimately fatal illness
- Food has one raising a little complaint
- Complaint about Democrat backing out of a ‘train crash’
- Pair heartily keen to drop a complaint
- Complaint: “Isn’t getting stuffed by Mel awful?”
- Fragment in meal, time for complaint
- Report of beer intended to generate complaint
Buddy explains!

The straight part
We know that "complaint" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case complaint = ailment.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 AILMENT mean?
AILMENT noun- Something which ails one; a disease; sickness.