This form, apparently present indicative active first person singular of a verb with stem θεει- is attested only here. From the gloss it would seem to be connected with a middle/passive infinitive θεεῖσθαι , defined at Apollonios Sophistes 86.18 as θαυμάζειν ('to marvel at'), and apparently (in Apollonios' view) related to the verb θεάομαι ('gaze at'). For reasons of accentuation and meaning it is less likely that the headword is a verbal derivative of either θεεῖον ('sulfur') or the late epic adjective θέειος , which is apparently a metrical expansion of θεῖος ('divine'), although the latter could conceivable produce a meaning appropriate to the present gloss ('I regard as divine', 'I hallow'). Cf. LSJ s.v. θέειον (web address 1).
Adler cites Lexicon Ambrosianum 202 as a comparandum.