Daniel 10:4

the first month Abib (Exodus 23:15), or (as it was called by the later Jews) Nisan (Nehemiah 2:1), the month in which the Passover (on the 14th day) and feast of Unleavened Cakes (15th 21st) were kept (Exodus 12:1-20). These sacred seasons thus fell within the period of Daniel's fast.

the great river elsewhere the Euphrates (Genesis 15:18; Joshua 1:4): here, of the Ḥiddeḳel(Genesis 2:14), i.e. the Tigris (Ass. Idiglator Idiḳlat): cf. the Syr. form Deḳlath. (Tigrisis probably a Persian modification of the same name, suggested by the Old Pers. tighri, arrow cf. [tighra, pointed, sharp], on account of the swiftness of its stream: see Delitzsch, Paradies, p. 170 ff., who cites Strabo, xi. 14, 8, διὰ τὴν ὀξύτητα, ἀφʼ οὗ καὶ τοὔνομα, Μήδων τίγριν καλούντων τὸ τόξευμα.)