The origin is uncertain as no reliable cognates are attested anywhere else in Semitic. In a purely theoretical perspective, one could venture to connect it with PWS *
ṭry ‘to be fresh, raw, wet’ W. von Soden (AHw. 663) tentatively compares Akk.
miṭirtu, miṭru ‘Wasserlauf,’ ‘a type of field or orchard characterized by a special irrigation system; a type of canal or ditch’. This comparison has been accepted in Dolgopolsky 1978:2 and Krebernik 2006:85. A more straightforward Akkadian cognate may be muṭṭuru ‘oozing moisture’ (Kouwenberg 1997:381, 414), not recognized by the standard dictionaries (cf. AHw. 572, CAD M₁ 11), but fitting the attested contexts well, both orthographically and semantically
Kogan 2015: 177