soft, sweet, and full-flavored from ripeness, as fruit.

well-matured, as wines.

soft and rich, as sound, tones, color, or light.

made gentle and compassionate by age or maturity; softened.

friable or loamy, as soil.

mildly and pleasantly intoxicated or high.

pleasantly agreeable; free from tension, discord, etc.

a mellow neighborhood.

affably relaxed; easygoing; genial

a mellow teacher who is very popular with her students.

to make or become mellow.

Slang . a state, atmosphere, or mood of ease and gentle relaxation. ?

mellow out, Slang .

to become detached from worry, strife, stress, etc.; relax

After final exams let's go down to the beach and mellow out.

to make more relaxed, agreeable, workable, etc.; soften or smooth

Chopin really mellows me out when I'm feeling tense.