We can review Zeno of Citium's "Analogy of the Closing Hand" for contrast (from Academica 2.145):
1. An open hand represents φαντασία (an appearance)
2. Partially closed fingers represent συγκατάθεσις (assent that the appearance is true)
3. A closed fist represents κατάληψις (thorough comprehension),
4. Finally, the other hand enclosing the fist represents ἐπιστήμη (understanding) – true knowledge, possessed only by the wise.
This is contrasted (Academica 2.142) with "a different judgment exists for Epicurus – who thinks all judgment is established in the senses, in the acquaintance with things, and in pleasure"
I think it's hiding in other forms within the texts.
Yes, Epicurus uses the verbal form of κατάληψις, for example at 10.78b he says:
"καὶ Τοῦτο Καταλαβεῖν τῇ διανοίᾳ ἔστιν ἁπλῶς εἶναι"
"...and to thoroughly comprehend with the mind that this [reality] exists is absolutely possible."
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10.125a. "Οὐθὲν γάρ ἐστιν ἐν τῷ ζῆνδεινὸν τῷ κατειληφότι γνησίως τὸ μηδὲν ὑπάρχειν ἐν τῷ μὴ ζῆν δεινόν"
"Nothing is terrible in living for the one who has thoroughly comprehended, in a genuine way, that nothing exists as terrible in not living."
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Philodemus, On Piety, 1.66A.1882-1911 "καὶ καθάπερ κἀν τῷ δευτέρῳ καὶ τριακοστῷ, καὶ τῶν θεῶν Ἐναργείαι, Φησὶν, καταλαμβάνεσθαι τὸ ὄν"
"and just as in the Second-and-Thirtieth [book 32 On Nature, Epicurus] says, the evident Realities of the gods are thoroughly comprehended as existing"
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Interestingly we have both prefixes in "προ-κατα-λαμβάνειν," which is best read as intensifying προ-λαμβάνειν (thus meaning "thoroughly anticipated" and not "comprehended")
VS 47 "Προκατείλημμαί σε – ὦ Τύχη!"
"I have thoroughly anticipated you – O Chance!"
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