As Latin became Old French, /vi/ & /bi/ between vowels unusually became /dʒ/ (the "j" sound). This has given English pairs like rabies/rage, lobby/lodge, salvia/sage, ruby/rouge, subservient/sergeant
rage comes from Old French rage, from Late Latin rabia, a regularization of Classical Latin rabies.
lobby and lodge are both from Late Latin laubia, a loanword from Frankish laubija, meaning "arbour" or "shelter".
sage (the plant) comes directly from its Latin name salvia. (As a sidenote, the psychedelic salvia is one of many salvia/sage species and is native to Mexico).
rouge is from Latin rubeus ("red"), while ruby is from Latin rubinus. This means that while ruby and rouge are closely related, they're not a neat doublet like the others.
The latter half of (sub)servient and sergeant are both from Latin servientem meaning "serving".
Other pairs include sapient/sage (meaning wisdom, as in sage advice) and cavity/cage (the latter from Latin cavea > *cavia).