Careen has undergone one of English's most complete semantic transformations, from a precise nautical procedure to a general verb for wild, uncontrolled movement. The original meaning was entirely technical: to careen a ship was to heave it onto its side, exposing the hull below the waterline for cleaning, repair, and recaulking. The word entered English from French carener, from Italian carenare, from carena ("keel"), ultimately from Latin carina ("keel, hull, nutshell").
Careening was essential maintenance in the age of wooden sailing ships. Marine organisms — barnacles, seaweed, shipworms — attached to hulls below the waterline, slowing vessels dramatically and, in the case of shipworms (Teredo navalis), actually boring through the planking. A heavily fouled ship might lose a third of its speed. Regular careening — tipping the ship, scraping the growth, and applying protective coatings of tallow, sulfur, or later copper sheathing — was critical to maintaining operational effectiveness.
Pirates and privateers had a particular relationship with careening. Unable to use official naval dockyards, they sought secluded beaches and coves — "careening places" — where they could beach their vessels, tip them on their sides, and perform maintenance undisturbed. Many Caribbean locations were named for this practice: Carénage Bay in Grenada, Carenero in Venezuela. A ship being careened was extremely vulnerable — heeled over, with guns dismounted and crew occupied — making careening places both essential and dangerous for anyone operating outside the law.
The modern meaning of careen — swerving, lurching, or rushing headlong — appears to result from confusion with "career" in its older verb sense of "to rush at full speed" (from French carrière, "racecourse"). A vehicle "careening around a corner" is actually "careering" in strict usage. However, the merger happened so long ago and so completely that most modern dictionaries accept both "careen" and "career" as verbs meaning to rush or swerve wildly. The nautical image of a ship heeled sharply to one side may have reinforced the association with tilting and instability.
In astronomy, the Carina constellation takes its name from the same Latin root — it represents the keel of the mythological ship Argo, which carried Jason and the Argonauts.