פָּשַׁת an unused root, perhaps i.q. Arabic فَشَّ to shake up, specially to card cotton (see Avic., in Castell.), Syriac carding. [Instead of this root there is given in Thes. פֵּשַׁשׁ.] Hence—
פִּשְׁתֶּה [in Thes פֵּשֶׁת] with suffix פִּשְׁתִּי Hosea 2: 7, 11 ; and פִּשְׁתָּה plur. פִּשְׁתִּים fem. ( Isa. 19:9 )—(1) flax , sing., Ex. 9:31 ; plur., Levit. 13:47 , seq.; Deut. 22:11 ; Isa. 19:9 ; Jerem. 13:1. פִּשְׁתֵּי הָעֵץ Josh. 2: 6, flax of tree, cotton (see the root), (both flax and cotton are also expressed in Syriac and Arabic by the same word, ىُتُنُ); but this is rendered by LXX., Vulg., Syr., stalks of flax, prop. flax of wood, or flax wood, which would rather be called עֲצֵי הַפִּשְׁתִּים.
(2) a wick made of flax or cotton, Isaiah 42:3 ; 43:17 . (Foster, De Bysso Antiqu., p. 63, considers פִּשְׁתֶּה to be of Egyptian origin, from ϢΕΑΤΣΙ, prop. thread plant, with the art, pi.).
Then, this makes its way into Akkadian as the loanword, kitû(m) "linen, flax" (This also appears as another loanword in Akkadian kitu(m) "mat," see AHw 495 for both entries. )
This word then appears in Northwest Semitic languages including biblical Hebrew where its form is kuttōnet "shirt-like tunic" according to HALOT 505 (HALOT mentions the word's Akkadian pedigre but does not mention its connection with Sumerian.)
Finally, this word appears in Greek and the New Testament form is kiton "tunic, shirt, cloths" BDAG 1085.