imperceptibly
From LSJ
Τοὺς δούλους ἔταξεν ὡρισμένου νομίσματος ὁμιλεῖν ταῖς θεραπαινίσιν → He arranged for his male slaves to have sex with female slaves at a fixed price (Plutarch, Life of Cato the Elder 21.2)
English > Greek (Woodhouse)
adverb
P. and V. λάθρα, λαθραίως (rare B.).
little by little: P. κατ' ὀλίγον, κατὰ βραχύ; see gradually.
do a thing imperceptibly: P. and V. λανθάνειν ποιῶν τι, V. λήθειν ποιῶν τι.