early 15c., "spring of water that collects in a pool," from Old French fontaine "natural spring" (12c.), from Late Latin fontana "fountain, spring" (source of Spanish and Italian fontana), from noun use of fem. of Latin fontanus "of a spring," from fons (genitive fontis) "spring (of water);" cognate with Sanskrit dhanvati "flows, runs."
The extended sense of "artificial jet of water" (and the structures that make them) is first recorded c.1500. "A French fountain-pen is described in 1658 and Miss Burney used one in 1789" [Weekley].