A good deal

[fredpuli47]

"A good deal of brandy was consumed" When and how did 'a good deal' come to mean 'a substantial quantity' and 'deal' by itself to mean 'a lot' or 'quite a lot', as in 'He is a deal of trouble' ?.

[Clanad]

One source has this:
"deal

from O.E. dæl "part, share, quantity," and its verbal derivative dælan "to divide," from P.Gmc. *dailaz ; also found in Balto-Slavic (cf. O.C.S. delu "part," Lith. dalis ). Meaning "to distribute cards before a game" is from 1520s; business sense is 1837, originally slang. Meaning "an amount" is from 1560s. New Deal is from F.D. Roosevelt speech of July 1932. Big deal is 1928; ironic use first recorded 1951 in "Catcher in the Rye." To deal with "handle" is attested from mid-15c. Deal breaker is attested by 1975. " (Source: Online Etymology Dictionary)

[Quizmonster]

To add a little to C's response above, the earliest recorded use of the specific three-word phrase, "a good deal"...spelt "a gode dele"...came from a recipe in a cookery book published in 1430. As it happens, salt was the ingredient involved.
(A buxom ex-colleague named Delia was always called Big Deal!)

[fredpuli47]

Ta. That all makes sense. So a 'good deal' was a good share or a good quantity and is a phrase which is a pretty old. The writer in 1560 must have known it would be readily understood.

[fredpuli47]

...as indeed must the cookery writer in 1430.