Definitions of decline:

• noun:   change toward something smaller or lower
• noun:   a condition inferior to an earlier condition; a gradual falling off from a better state
• noun:   a gradual decrease; as of stored charge or current
• noun:   a downward slope or bend
• verb:   go down

  Example: "The roof declines here"

• verb:   grow smaller
• verb:   inflect for number, gender, case, etc., "in many languages, speakers decline nouns, pronouns, and adjectives"
• verb:   go down in value
• verb:   show unwillingness towards

  Example: "He declined to join the group on a hike"

• verb:   grow worse
• verb:   refuse to accept