mettlesome

The 17th-century adjective mettlesome (popularly used of spirited horses) sometimes appeared as the variant metalsome. That's not surprising. In the 16th century and for some time after, mettle was a variant spelling of metal—that is, the word for substances such as gold, copper, and iron. The 16th century was also when metal—or mettle—acquired the figurative sense of "spirit," "courage," or "stamina." However, by the early 18th century, dictionaries were noting the distinction between metal, used for the substance, and mettle, used for "spirit," so that nowadays the words mettle and mettlesome are rarely associated with metal.