Resembling lightning or flashing brilliantly; characterized by sudden bursts of light (British variant).
From fulgour (British spelling of fulgor) plus the English suffix -ous. This represents the British variant of fulgorous, maintaining the -our spelling throughout. Both fulgorous and fulgourous are valid but extremely rare in modern English.
This is an example of how archaic British spellings can layer on top of each other—fulgourous keeps the -our from British orthography even when adding the -ous suffix. Most modern speakers would just say 'brilliant' instead!
Complete word intelligence in one call. Free tier — 50 lookups/day.