/ grɒg; NAmE grɑːg/ noun [ U ]
1.
a strong alcoholic drink, originally rum , mixed with water
2.
( informal , AustralE , NZE ) any alcoholic drink, especially beer
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WORD ORIGIN
mid 18th cent.: said to be from Old Grog , the reputed nickname of Admiral Vernon (1684–1757), who in 1740 first ordered diluted (instead of neat) rum to be served out to sailors.