The most common and most likely answer to this crossword clue is the 7 letter word HEALTHY
I've seen this crossword clue in The Daily Telegraph
H
E
A
L
T
H
Y
More clues leading to the result HEALTHY
Buddy explains!
The straight part
We know that "well" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case well = healthy.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 HEALTHY mean?
HEALTHY adjective- Enjoying health and vigor of body, mind, or spirit: well.
- Conducive to health.
- Evincing health.
- Significant, hefty; beneficial.