The antonym for "bought a one-way ticket" could be "bought a round-trip ticket." This would suggest that the person intends to return to their starting point after their journey. Another possible antonym could be "canceled the ticket," indicating that the person has decided not to go on the trip after all. Alternatively, the antonym could be "received a return ticket," indicating that the person was given a free or complementary ticket back home. These various antonyms highlight the diverse meanings and possibilities contained within the phrase "bought a one-way ticket," which can imply both freedom and uncertainty in equal measure.