The headword is a feminine noun (tmh=sis, -ews, h(/) given here in the nominative singular; see generally LSJ s.v. (and for cognates cf. tau 712, tau 713, tau 714, tau 715, tau 717, tau 718). No equivalent entry in other lexica, but ps.-Zonaras glosses the headword with diai/resis.
There are several instances of the headword in Plato (Symposium 190E, Republic 470A, Politicus 276D), and see also e.g. Aristotle, De anima 412b28 (the strange, but somehow elucidating, comparison of the actuality of wakefulness to the cutting of an axe).
[1] The gloss is an articular substantivization (Smyth, §1153) of the adjective tomo/s, -h/, -o/n (cutting, sharp); see LSJ s.v.