The number one meaning for this word as an adjective is clearly: on fire, illuminated, lit up.
By the time the fire brigade got to the old house, it was completely alight.
What always amused me as a child was to see this word used as a verb to mean get off or out of transport, usually public transport. It is a rather formal almost jargon-like term often used to give a legal tone.
Push button to alight.
Alighting passengers should use the rear exit.
The press are at the convention centre waiting for the President to alight.
By now you will realise that this word has to do with lighten or make less heavy, but in my young mind I started to see my fellow passengers bursting into flames.