The word 'Enlightened' comes from the Latin prefix 'en' meaning 'in, or into', and the word 'lux' meaning 'light', so :
In or Into The Light.
In a spiritual context the concept of 'The Light' is often used to signify the Light of 'Divine Truth'.
Words used to describe 'The Light' include : Absolute, Eternal, Infinite - and Unconditional Love.
Using these criteria, Enlightenment would be : the moment of 'Becoming One with The Light'.
It is said...
The moment of Enlightenment is experienced as an irreversible 'flowing-in' of 'The Light'.
The moment when the 'known' reality of the 'self' is instantaneously shown to have been entirely false.
It is then known with absolute certainty that this 'flowing-in of unconditional love' is the 'completion' of the 'self'.
It is realised that this is true Enlightenment - and it is the conclusion and destination of the Inner Journey of the 'self'.