jell v.

late 14c., gelee, gelle, gelly, "semisolid substance from animal or vegetable material, spiced and used in cooking; chopped meat or fish served in such a jelly," from Old French gelee "a jelly," also "a frost," noun use of fem. past participle of geler "to congeal, to freeze," from Latin gelare "to freeze, congeal, stiffen," related to gelu "frost," from PIE *gela-, suffixed form of root *gel- "cold; to freeze."

By early 15c. it was used of any jellied or coagulated substance; from 16c. as "thickened juice of a fruit prepared as food."

"semi-solid substance," 1899, as a chemical term, short for gelatin and perhaps influenced by jell. The invention of this word is credited to Scottish chemist Thomas Graham. Hair-styling sense is from 1958.

Proto-Indo-European root meaning "cold; to freeze." 

It forms all or part of: chill; cold; congeal; cool; gel; gelatine; gelatinous; gelato; gelid; glace; glacial; glaciate; glaciation; glacier; glaciology; glacis; jell; jelly.

It is the hypothetical source of/evidence for its existence is provided by: Latin gelare "to freeze," gelu "frost," glacies "ice;" Old English cald "cold, cool," German kalt.