ירדן

Likely, from a Proto-Semitic root denoting “to descend”, “to go or come down”, “to stream down”, “to come down to water”, “a place descending to water”, “a watering place”; cognates found Arabic وَرَدَ (warada, “to go down or come upon water”), Hebrew יָרַד (yāráḏ, “to go down”), Aramaic ירד (yreḏ, “stream”), and Ge'ez ወረደ (wärädä, “fall down, go down, drain off, pour down”), and Akkadian 𒉿𒊏𒁺𒌝 (warādum, “to go down to lower ground, to come ashore, to go downhill or downstream”).
Dubiously, Ludwig Köhler has affirmed as a final interpretation a compound from Proto-Iranian *yáHr̥ (“year”), from Proto-Indo-Iranian *yáHr̥, from Proto-Indo-European *yeh₁- (“year”) (compare Avestan 𐬫𐬁𐬭𐬆 (yār^ə, “year”)) and Proto-Iranian *dānu (“river”) (< Proto-Indo-Iranian *dáHnu < Proto-Indo-European *déh₂nu) (compare Ossetian дон (don, “river”), Avestan 𐬛𐬁𐬥𐬎 (dānu, “river”)), according to which the Jordan is the “year-river” because of its water level being consistent the whole year, backing this derivation by the theory that the name of the Orontes is of “certain” Iranian origin, although also found attested earlier. This is however unlikely, as the name “Yārdon” is found attested at the period of Ramesses II in the Papyrus Anastasi I, making the Semitic origin much more probable.

הַיַּרְדֵּן • (hayyardén) m

Jordan (a river in Western Asia, in the Middle East, that empties into the Dead Sea, flowing through Israel, the Golan Heights, the West Bank and Jordan)

יַרְדֵּן • (yardén) m or f

Köhler, Ludwig (1939) “Lexikologisch-Geographisches”, in Zeitschrift des Deutschen Palästina-Vereins‎^[1] (in German), volume 62, number 1, pages 115–120

Yiddish

ירדן • (yarden) m