κατανοητέον
From LSJ
Τὰς γὰρ ἡδονὰς ὅταν προδῶσιν ἄνδρες, οὐ τίθημ' ἐγὼ ζῆν τοῦτον, ἀλλ' ἔμψυχον ἡγοῦμαι νεκρόν → But when people lose their pleasures, I do not consider this life – rather, it is just a corpse with a soul
English (LSJ)
A one must observe, learn, Pl.Plt.305c, Porph.Marc.27; one must consider, πάλιν περί τινος Ph.1.83.
Greek (Liddell-Scott)
κατανοητέον: ῥημ. ἐπίθ., πρέπει νὰ μάθῃ τις, νὰ παρατηρήσῃ, Πλάτ. Πολιτ. 305C.
Dutch (Woordenboekgrieks.nl)
κατανοητέον, adj. verb. van κατανοέω, men moet beseffen.