It seems that you have missed the necessary options for us to complete this analogy, but hope this one helps. So if thread is to string, therefore, a cask is to barrel. A cask is a <span>large barrel like container made of wood, metal, or plastic, used for storing liquids especially those with alcohol. Hope this answers the question.</span>
The first two words "Thread and string" are related because both of them are synonyms. Thus, the word that is similar to cask needs to be a synonym in order to match to the comparison of the other two words.
