μὴ ἐν πολλοῖς ὀλίγα λέγε, ἀλλ΄ ἐν ὀλίγοις πολλά → don't say little in many words, but much in a few words (Stobaeus quoting Pythagoras)
Celt, Kelt = Κέλτης
Celts, Kelts, Celtae = Κελτοί, οἱ, Κελταί, οἱ.
Celtic, Keltic, adj.: Κελτικός.