The most common and most likely answer to this crossword clue is the 7 letter word MILDEST
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The straight part
We know that "Extremely gentle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case extremely gentle = mildest.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 MILDEST mean?
MILDEST adjective- Gentle and not easily angered.
- (of a rule or punishment) Of only moderate severity; not strict.
- Not overly felt or seriously intended.
- (of an illness or pain) Not serious or dangerous.
- (of weather) Moderately warm, especially less cold than expected.
- (of a medicine or cosmetic) Acting gently and without causing harm.
- (of food, drink, or a drug) Not sharp or bitter; not strong in flavor.