为什么phantom与fantastic是同一词源，但第一个辅音的写法不同？

谢邀。

fantastic (adj.)

late 14c., "existing only in imagination," from Middle French fantastique (14c.), from Medieval Latin fantasticus, from Late Latin phantasticus "imaginary," from Greek phantastikos "able to imagine," from phantazein "make visible" (middle voice phantazesthai "picture to oneself"); see phantasm. Trivial sense of "wonderful, marvelous" recorded by 1938. Old French had a different adjective form, fantasieus "weird; insane; make-believe." Medieval Latin also used fantasticus as a noun, "a lunatic," and Shakespeare and his contemporaries had it in Italian form fantastico "one who acts ridiculously."

phantom (n.)

c. 1300, fantum "illusion, unreality," from Old French fantosme (12c.), from Vulgar Latin *fantauma, from Latin phantasma "an apparition" (see phantasm). The ph- was restored in English late 16c. (see ph). Meaning "specter, spirit, ghost" is attested from late 14c.; that of "something having the form, but not the substance, of a real thing" is from 1707. As an adjective from early 15c.

ph

now in English usually representing "f," originally it was the combination used by Romans to represent Greek letter phi (cognate with Sanskrit -bh-, Germanic -b-), which at first was an aspirated "p," later the same sound as German -pf-. But by 2c. B.C.E. had become a simple sound made by blowing through the lips (bilabial spirant).

Roman "f," like modern English "f," was dentilabial; by c. 400, however, the sounds had become identical and in some Romanic languages (Italian, Spanish), -ph- regularly was replaced by -f-. This tendency took hold in Old French and Middle English, but with the revival of classical learning the words subsequently were altered back to -ph- (except fancy and fantastic), and due to zealousness in this some non-Greek words in -f- began to appear confusedly in -ph-, though these forms generally have not survived.