Tranquillize comes from tranquil + -ize; tranquil is from Latin tranquillus ('calm, quiet'), perhaps from trāns ('across, through') + a root related to quiēs ('rest'). The historical chain includes Latin tranquillus. The quoted older senses, "calm, quiet", "across, through", and "rest", supply the semantic anchors for tranquillize. The formation is best read as suffixal, compound, and borrowed: the word tranquillize carries its older form-history into a compact English lexical shape. In present English it is used as a verb, "to make calm or sedate, especially with a drug". English derivatives include tranquillizer, tranquillized, and tranquillizing; related English forms include tranquil and tranquillity. The result is a verb whose etymology preserves both the older form and the later English specialization.