Provenance
Where it comes from.
'Neon' was coined in 1898 by the chemists who isolated the gas, from Greek neos, 'new,' because it was newly found. Its glow entered daily life within a generation: neon advertising appeared by 1913 and the 'neon sign' was a fixture by 1927, tying the word permanently to bright light and city nights.
The ending '-plex' is drawn from words like complex and multiplex, where it carries the sense of many parts interwoven into one place. Joined to neon, it names not a single lamp but a whole lit-up destination.