luncheon
Concise Oxford English Dictionary © 2008 Oxford University Press:
luncheon/ˈlʌntʃən/
▶noun formal lunch.
– origin C16 (in the sense ‘thick piece, hunk’): possibly an extension of obs. lunch ‘thick piece, hunk’, from Sp. lonja ‘slice’.
'luncheon' also found in these Oxford entries:

