freneza

Freneza runs from clinical insanity to the loose everyday sense of a daft idea, but it sits harder than English "crazy" does, so use it about people with some care. The family is regular and worth having: frenezulo is a madman, frenezeco is madness, frenezigi is to drive somebody mad and freneziĝi is to go mad yourself. For something merely odd, stranga is the word you want; freneza is a judgement, not an observation.