mos.

From Proto-Italic *mōs, a root noun interpreted as an s-stem noun, of uncertain origin. Generally believed to derive from Proto-Indo-European *moh₁-, *meh₁- (“to intend or be intent upon, to be of strong will”) (though the more common meaning of “to measure” may be the original, with “to intend” as a semantic extension), whence Ancient Greek μαίομαι (maíomai, “to strive”) and perhaps Ancient Greek Μοῦσᾰ (Moûsă, “Muse”), and also English mood. It has also been conjectured that some senses of mōs, such as those having to do with “manner” and “way”, may indicate a possible derivation from Proto-Indo-European *med- (“to measure”), compare and contrast modus; if that is true, it would seem to suggest an example of combined etymology or conflation. If two such roots *med- and *meh₁- existed, both meaning “to measure”, it is plausible that the latter was derived from the former via early PIE glottalic *d ~ *h₁ alternation, seen for example in the pair *dwi- : *h₁wi- (“in two; apart”) and possibly in other roots such as *wed- : *weh₁- (“to wet; water”); *h₂ed- : *h₂eh₁- (“to dry (by fire)”).