MINOR

Of lesser importance or stature or rank

Example: "A minor poet"

Lesser in scope or effect

Example: "Had minor differences"

Inferior in number or size or amount

Example: "A minor share of the profits"

(of a scale or mode) having half steps between the second and third degrees, and (usually) the fifth and sixth degrees, and the seventh and eighth degrees

Example: "The minor keys"

Not of legal age

Example: "Minor children"

Of lesser seriousness or danger

Example: "Suffered only minor injuries"

Of your secondary field of academic concentration or specialization