English translation (word)
English translation (etymon)
Ὡς μὲν Ποσειδώνιος, παρὰ τὸ ἅπτω ἅψω, ἁψίς τις οὖσα, ἡ φῶς ἐμποιοῦσα καὶ καταυγάζουσα τῶν ὑποκειμένων ἕκαστα, ὡς πῦρ· ὡς δέ τινες, παρὰ τὸ ἅπτω, τὸ συνάπτω, ἁψὶς καὶ ὀψὶς, ἢ διὰ τῶν ὁρατῶν ψαῦσιν ποιουμένη πρὸς κατανόησιν. Ἢ παρὰ τὸν ὄψω μέλλοντα.
As Posidonius says, from haptō "to kindle", <future> hapsō, a hapsis "kindling", so to speak, that which produces light and illuminates each of the things it touches, as fire does. But for some, it comes from haptō "to touch", hapsis "touching" and opsis "sight", that which, because it touches the visible things, produces understanding. Or from the future opsō "I will see".
The link with ὄψομαι is correct, although of course ὄψις is not directly derived from the future stem. Starting from the future was a usual way to account for suffixes with [s] in Greek grammar.
Ps.-Zonaras, Lexicon, omicron, p. 1494 (Ὄψις. διάκρισις χρωμάτων [καὶ σχημάτων] καὶ ὄγκων. παρὰ τὸ ἅπτω, τὸ συνάπτω, ἅψις καὶ ὄψις. ἡ διὰ τῶν ὁρατῶν ψαῦσιν ποιουμένη πρὸς κατανόησιν. ἢ παρὰ τὸν ὄψω μέλλοντα)