When a pair of words has entered a language through different routes and each of the words came from the same etymological root the words are considered linguistic doublets (sometimes called "etymological twins").
Doublets occur in languages either because each of the individual words was borrowed from a single source language at a different stage in time, or because one of the words was borrowed from a main language and the other was borrowed from that language's daughter language.
Following are some examples of linguistic doublets that are listed on Wikipedia:
shirt and skirt (both Germanic, the latter from Old Norse)
chief and chef (both from French at different times)
secure and sure (from Latin, the latter via French)
plant and clan (from Latin, the latter via Old Irish)
ward and guard (from Norman, the latter via French); also warden and guardian.
frenetic and frantic (both from Greek, via Old French and Latin)
cave and cavern (from Latin 'cavus', via Fench and Germanic languages respectively)
By the way, for some odd reason whenever I hear about doublets the Wrigley's Doublemint Gum song pops into my head.