Completely, for good: verb + hẳn

After a verb, hẳn means "completely" or "for good": the change is total and won't be undone. Ba tôi bỏ hẳn thuốc lá rồi. My dad has given up smoking for good. Năm sau chị về hẳn Việt Nam. Next year I'm moving back to Vietnam for good. Khỏi hẳn is to be fully better: Em khỏi hẳn chưa?

After an adjective, with đi or ra, hẳn says a change is clear for all to see, "noticeably": Sơn lại xong, căn nhà nhìn đẹp hẳn ra. After repainting, the house looks so much nicer. Đi goes with losing something (thinner, older, quieter), ra with gaining (healthier, prettier, younger).

In Saigon ốm means "thin", so ốm hẳn đi is "has got much thinner". In Hà Nội the word is gầy: gầy hẳn đi.

Hẳn before a verb, usually as chắc hẳn or hẳn là, means something else, "surely, must be": Chắc hẳn chị mệt lắm. You must be very tired.