The morphological and semantic interpretation of ἀδηίζω on the Theran ‘pact of the first settlers’ (SEG 9, 3.39, Cyrene, 370-360 BCE) is controversial. In this paper, after discussing other previously proposed hypothesis, I will argue that ἀδηίζω derives from an unattested *ἀδεής ‘invisible’, a determinative compound derived from *deih2- ‘appear, seem’. The deadjectival ἀδηίζω is therefore semantically equivalent to ἀδηλόω and ἀφανίζω ‘render invisible’