Probably from an unused root meaning to give; a present (for prostitution) -- gift.
H5083. nadan
I. [נֹ֫דֶן נֶ֫דֶן, נָדָן,]
noun [masculine] gift (probably Assyrian loan-word, compare Assyrian nudnu, dowry DlHWB 451, √ nadânu = נתן, DlBaer Ezech.xiv); — נְדָנַיִךְ Ezekiel 16:23, of bribe from harlot ("" נֶ֑דֶה), metaphor of Jerusalem.