means The whole of what makes you you — your identity, your inner being, the continuous person you experience yourself to be.

from From Old English 'self' (also 'seolf,' 'sylf'), a Germanic word — kin to Old Norse 'sjalfr,' Dutch 'zelf,' and German 'selbst.' For most of its life it was just an intensifier or reflexive ('the king himself,' 'wash yourself'), and only later did English start treating it as a noun — a thing you could have, find, lose, and discover. The bigger ancestry beyond Germanic is murky, so where 'self' ultimately comes from is, fittingly, a question of identity that nobody has fully answered.