Unusual, unconventional, or idiosyncratic.

Not officially established. / Implicitly true but withheld and/or contradicted by authority. / Not acting with official authority. / (pharmacology) Not listed in a national pharmacopeia etc.

not yet opened; still closed

Not noticeable or blatant; inconspicuous.

(cricket) A style of bowling used by a left-handed bowler in which wrist spin is used to move the ball from off to leg (for a right-handed batsman).

A method of studying social behavior indirectly, without affecting it.

(literally) Any entrepreneur who uses unorthodox business practices / (by extension) Anyone who carries on an illegal business e.g. a drug dealer or prostitute

(of a house etc) Not inhabited, especially by a tenant / Not being used; vacant or free / Not employed on a task; idle / (of territory) Not occupied by foreign troops etc

Not seen or observed.

whilst not being seen or observed