DOUBLET
One of two (or more) words in a language that have the same etymological root (as in etymon, not root morphemes like Proto-Indo-European roots) but have come to the modern language through different routes.
Doublets can come about e.g., as loanwords from two different but related languages, as loanwords acquired from the same language at two different stages, as one loanword from a related language plus its native cognate, or as derivatives formed at two different stages in the history of a language.
Example: lever and levator are doublets (more at Category:English doublets).