It descends from the word seen in Zoroastrian Middle Persian as <
khwbn> /kahwan/ and in Manichaean Middle Persian as <
qhwn>. Cognates include Parthian <
kfwn>, Balochi
kwahn, etc., Bactrian καββογο, and Khotanese
kuhana-.
According to Bailey,
Dictionary of Khotanese Saka, p. 64, the root etymology is Iranian *
kap-/*kaf- "to fall, befall, strike down" (Manichaean MP
kp-, kf-, qf-, Kurmanji
ketin, kev-, Zazaki
kewtiş, kewn-, Balochi
kapt-, kap-, kab-, all "to fall", but without verbal reflexes in New Persian). Iranian *
kafvana-, as Bailey reconstructs it, would be *"fallen" > "old".
Further Indo-European cognates would include Greek κόπτω "I strike, cut (off)", Lithuanian
kapiù (
kàpti) "I chop, fell (a tree)", and Albanian
kep- "to hew, chisel". All these suggestion a Proto-Indo-European root PIE *
kop-, "to fell, chop".
Also note the existence of a homophonous root *
kap-/*kaf- "to split" in Iranian ( New Persian کافتن ), from PIE *
skobh- "to shave off, split (or the like)" (seen in Latin
scabō "I scratch, rub", Lithuanian
skabaũ (
skabýti) "to pick off flowers, leaves, defoliate; to tear",
skobiù, skabiù (
skõbti) "to cut, carve, hollow out (wood)", Goth.
skaban "to shear", Old English
scafan, English
shave).
Cheung,
Etymological Dictionary of the Iranian Verb, p. 233f, notes that in Iranian it is difficult to separate this root *
kap/f- "fall" (< PIE *
kop- "to chop, fell a tree") from *
kap-/*kaf- "to split, shave" (from PIE *
skobh-):
They may originally refer to the (PIE) stages of [carpentry], first the felling of the tree (IE *kop- ‘to chop, fell’) and subsequently the cleaning and carving of the fallen tree into logs and planks (IE *skobh- ‘to pick clean, get rid of leaves; to split, shave’). These stages appear to be faithfully preserved in Lithuanian. The formal and semantic similarity of the two *kap/f- roots in many IE languages is no doubt the result of (mutual) interference. This may explain the disappearance of initial *s- in *kap/f.