cask / casque are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
cask: (noun) the quantity a cask will hold.
casque: (noun) (15-16th century) any armor for the head; usually ornate without a visor.
cask: k·AE·s·k
casque: NA
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)