The headword, evidently extracted from somewhere, is the aorist infinitive of the middle-voice verb tekmai/romai, I infer, demarcate; see LSJ s.v., and cf. tau 243 (and a compound form at sigma 1628).
[1] The genitive of source (Smyth §1410).
[2] This is the contract verb tekmhrio/w, I prove positively; see LSJ s.v. (Outside lexicography, this exact form -- first person singular, present indicative (and subjunctive) active -- appears only in Gregory of Nazianzus' poem De vita sua (62), but the lexica are using it as a generic paradigm.)
For the headword itself cf. Syntacticum Laurentianum 66.8-15; Etymologicum Gudianum 524.24-6; Etymologicum Magnum 750.18-19 (Kallierges).