The full, undiluted strength of whisky or other spirits after ageing; (hence) a whisky or other spirit bottled at full strength, directly from the cask; frequently attributive or as postpositive.
Origin
1970s; earliest use found in The Irish Times.
Definition of cask strength in US English:
cask strength
noun
The full, undiluted strength of whisky or other spirits after ageing; (hence) a whisky or other spirit bottled at full strength, directly from the cask; frequently attributive or as postpositive.