Origins
Abandon began as an act of generosity, not desertion.βββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ The Old French phrase Γ bandon meant 'at one's disposal' β to abandon something was to place it freely under another's authority. The word only soured over centuries into its modern sense of forsaking.
The core element bandon derives from Frankish *ban, a proclamation or command, itself from Proto-Germanic *bannanΔ . This root produced a remarkable constellation of English words. A ban is a formal prohibition β originally a public proclamation. To banish is to send someone away by proclamation. A bandit, through Italian bandito, was a person formally declared outside the law.
Development
Contraband completes the family: goods that go 'against the ban', smuggled in defiance of official decree.
The noun form β 'with reckless abandon' β preserves the oldest sense most faithfully. To act with abandon is to act as though you have surrendered all restraint, placed yourself entirely at the disposal of the moment. It is freedom through surrender, which is precisely what the Old French phrase described.