Wildly unconventional; bizarre; absurd.
Of a person's behaviour: greatly inappropriate.
Not normal; odd, unusual, surprising, out of the ordinary.
Outside of one's current relationship; unfamiliar.
Having the quantum mechanical property of strangeness.
Not belonging to one.
Unfamiliar, not yet part of one's experience.
Of an attractor: having a fractal structure.
Sex outside of one's current relationship.