gʷʰer-
“warm, hot, heated”warm, heated
Root for warmth. Gives English "warm", Latin formus "warm", Greek thermós.
Discussion
*gʷʰer- is the Proto-Indo-European root meaning "warm, hot." It is one of the primary PIE roots for thermal concepts, with reflexes across most branches of the family.
In Germanic, the root underwent Grimm's Law (*gʷʰ > w), yielding Proto-Germanic *warmaz, whence English "warm" and German warm. The verbal derivative *gʷʰer- also produced English "burn" (via Old English beornan, with metathesis from an earlier *brinnan, though some scholars connect "burn" instead to a separate root *bʰrewh₁-).
In Latin, *gʷʰer- gave formus "warm" (compare thermae from the Greek borrowing) and fornāx "furnace, oven." Greek θερμός (thermós) "hot" is the most recognizable reflex, surviving in English loans such as "thermal," "thermometer," and "thermos." Sanskrit gharmá- "heat" and Avestan garəma- "hot" show the expected satem reflex.
The root also appears in Slavic as Old Church Slavonic gorěti "to burn." The breadth of this root's descendants — from everyday English "warm" to scientific terminology like "thermodynamics" — illustrates how a single PIE root can ramify across registers and millennia of linguistic change.
Notes
Source of "thermal", "thermometer"; English "furnace" via Latin
Related Roots
English Words from *gʷʰer-
These modern English words descend from this root. Each page traces the full journey from PIE to present-day English.