δυσ-
From LSJ
Δελφῖνα νήχεσθαι διδάσκεις: ἐπὶ τῶν ἐν ἐκείνοις τινὰ παιδοτριβούντων, ἐν οἷς ἤσκηται → Teaching dolphins to swim: is applied to those who are teaching something among people who are already well versed in it
English (LSJ)
insepar. Prefix, opp. εὖ,
A un-, mis-, with notion of hard, bad, unlucky, etc., as δυσήλιος, δύσαγνος; destroying the good sense of a word, or increasing its bad sense: hence, joined even to words expressing negation, as δυσάμμορος, δυσανάσχετος; poet. in strong contrasts, as Πάρις Δύσπαρις, γάμος δύσγαμος. Before στ, σθ, σπ, σφ, σχ, the final ς was omitted, v. δυστ-. (Cf. Skt. du[snull ]-, dur-, e.g. durmanās, = δυσμενής; ONorse tor-, e.g. torsóttligr (δύσμαχος); OIr. du-, do-, e.g. dochruth 'misshapen'.)
