Catholicon (from Greek Καθολικόν 'universal') is a 15th-century dictionary written in Breton, French, and Latin. It is the first Breton dictionary and also the first French dictionary. It contains six thousand entries and was compiled in 1464 by the Breton priest Jehan Lagadeuc. It was printed in 1499 in Tréguier. A manuscript of the dictionary is preserved in the national library in Paris, identified as Latin 7656.

This Catholicon is referred to by some historians as the Catholicon Armoricum, in reference to Armorica, which is a name for Brittany in Latin. It is a different dictionary than the Catholicon Anglicum, which is an English-Latin dictionary compiled at very nearly the same time in England. The Catholicon Armoricum is also to be distinguished from the Catholicon of John of Genoa, a dictionary dated late 13th century written in Italy.