It forms all or part of: compass; El Paso; expand; expanse; expansion; expansive; fathom; pace (n.); paella; pan (n.); pandiculation; pas; pass; passe; passim; passacaglia; passage; passenger; passport; paten; patent; patina; petal; spandrel; spawn.
It is the hypothetical source of/evidence for its existence is provided by: Greek petannynai "to spread out," petalon "a leaf," patane "plate, dish;" Old Norse faðmr "embrace, bosom," Old English fæðm "embrace, bosom, fathom," Old Saxon fathmos "the outstretched arms."
"mass of fish eggs," mid-15c., roughe, probably from an unrecorded Old English *hrogn, from Proto-Germanic *khrugnaz (source also of Old Norse hrogn, Danish rogn, Swedish rom, Flemish rog, Middle Low German and Middle Dutch roge, Old High German rogo, German Rogen "roe"), from PIE *krek- "frog spawn, fish eggs" (source also of Lithuanian kurklė, Russian krjak "spawn of frogs"). The exact relation of the Germanic words to each other is unclear, and the Middle English word might be rather from Middle Dutch.
edible fish of the North Atlantic (Scomber scombrus), c. 1300, from Old French maquerel "mackerel" (Modern French maquereau), of unknown origin; perhaps so called from the dark blotches with which the fish is marked, from Latin macula "spot, stain" (see macula). But the word is apparently identical with Old French maquerel "pimp, procurer, broker, agent, intermediary" (itself attested in English in this sense by early 15c.), a word from a Germanic source (compare Middle Dutch makelaer "broker," from Old Frisian mek "marriage," from maken "to make").
The connection would be obscure, but medieval people had imaginative notions about the erotic habits of beasts. The fish approach the shore in shoals in summertime to spawn. Exclamation holy mackerel is attested from 1876.