I came across the word "tephra" here:
Barren Island, Andaman Islands, India
Quote:

dense clusters of incandescent tephra of various sizes were ejected from the crater



my dictionary gave me this:
Quote:

tephra |'tefr?| noun
Geology
rock fragments and particles ejected by a volcanic eruption.
ORIGIN 1940s: from Greek, literally ‘ash, ashes.’



I thought, cool, neat word. further digging (via OneLook, et. al.) got me to M-W, and this:
Quote:

Etymology: New Latin, from Greek, ashes; akin to Sanskrit dahati it burns -- more at FOMENT



my question (are you still with me? ) is this:
how do tephra and dahati relate? not to mention foment? those three words seem so far apart in spelling, that I can see no link.

(sorry, I can't get the schwa to show in the pronunciation...)

formerly known as etaoin...