'unexpectedly-stable' is a compound word formed from 'unexpectedly' and 'stable'. 'Unexpectedly' originates from the Latin word 'exspectare', meaning 'to look out for', and 'stable' comes from the Latin 'stabilis', meaning 'firm'.

'Unexpectedly' evolved from the Old French 'especter', while 'stable' transitioned from the Old French 'stable', eventually forming the modern English compound 'unexpectedly-stable'.

Initially, 'unexpectedly' meant 'not foreseen', and 'stable' meant 'firm or steady'. Together, they convey the idea of something being steady against expectations.