"flat-bottomed boat" (especially, in military engineering, one to support a temporary bridge over a river), 1670s, from French pontoon, from Old French ponton (14c.) "bridge, drawbridge, boat-bridge; flat-bottomed boat," from Latin pontonem (nominative ponto) "flat-bottomed boat," from pons "bridge" (see pons). Pontoon bridge "roadway supported on pontoons" is recorded by 1778. Related: Pontooneer (n.).
"bridge," in anatomy and in various Latin expressions, from Latin pons "bridge, connecting gallery, walkway," earlier probably "way, passage," from PIE root *pent- "to go, tread" (see find (v.)). Especially pons asinorum "bridge of asses," nickname since early 16c. for the fifth proposition of the first book of Euclid, which students and slow wits find difficulty in "getting over": if two sides of a triangle are equal, the angles opposite these sides also are equal. "The original allusion seems to have been to the difficulty of getting asses to cross a bridge" [Century Dictionary]. The Latin word is the source of Italian ponte, French pont, Spanish puente.
member of the supreme college of priests in ancient Rome, 1570s, from Latin pontifex "high priest, chief of the priests," probably from pont-, stem of pons "bridge" (see pons) + -fex "maker," from facere "to do, make" (from PIE root *dhe- "to set, put").
If so, the word originally meant "bridge-maker," or "path-maker." It was felt as such; the sense of "bridge-builder" was in the Medieval Latin word, and Milton uses pontifical (adj.) in this sense. Sense was extended in Church Latin to "a bishop," in Medieval Latin to "the Pope." In Old English, pontifex is glossed in the Durham Ritual (Old Northumbrian dialect) as brycgwyrcende "bridge-maker."
Weekley points out that, "bridge-building has always been regarded as a pious work of divine inspiration." Century Dictionary speculates it had its origins as "having charge of the making or maintenance of a bridge — it is said of the Sublician bridge built over the Tiber by Ancus Marcius." Or the term may be metaphoric of bridging the earthly world and the realm of the gods. Other suggestions trace it to Oscan-Umbrian puntis "propitiary offering," or to a lost Etruscan word; in either case it would have been altered by folk etymology to resemble the Latin for "bridge-maker."
["doorkeeper, janitor"] mid-13c. (late 12c. as a surname), "one who has charge of a door or gate; one who guards the gate of a bridge," from Anglo-French portour, Old French portier "gatekeeper" (12c.), from Late Latin portarius "gatekeeper," from Latin porta "city gate, gate; door, entrance," from PIE root *per- (2) "to lead, pass over."
Under the brown fog of a winter dawn,
A crowd flowed over London Bridge, so many,
I had not thought death had undone so many.
[Eliot, from "The Waste Land," 1922]