The most common and most likely answer to this crossword clue is the 6 letter word MELLOW
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The straight part
We know that "Mature" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mature = mellow.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 MELLOW mean?
MELLOW noun- A relaxed mood.
- To make mellow; to relax or soften.
- To become mellow.
- Soft or tender by reason of ripeness; having a tender pulp.
- Easily worked or penetrated; not hard or rigid.
- Not coarse, rough, or harsh; subdued, soft, rich, delicate; said of sound, color, flavor, style, etc.
- Well matured; softened by years; genial; jovial.
- Relaxed; calm; easygoing; laid-back.
- Warmed by liquor, slightly intoxicated, stoned, or high.