Definitions of mellow:

• verb:   make or grow (more) mellow

  Example: "These apples need to mellow a bit more"

• verb:   become more relaxed, easygoing, or genial

  Example: "With age, he mellowed"

• verb:   soften, make mellow

  Example: "Age and experience mellowed him over the years"

• adjective:   having attained to kindliness or gentleness through age and experience

  Example: "Mellow wisdom"

• adjective:   having a full and pleasing flavor through proper aging

  Example: "A mellow port"

• adjective:   having or suggesting softness and richness in quality

  Example: "A mellow sound"

• adjective:   slightly and pleasantly intoxicated from alcohol or a drug (especially marijuana)
• adjective:   unhurried and relaxed

  Example: "A mellow conversation"

• adverb:   (obsolete) in a mellow manner
• name:  A surname (very rare: popularity rank in the U.S.: #39890)