In 1632 the group began to assemble the most extensive set of Irish annals ever compiled. The project took four years and resulted in the vast collection dubbed "Annála Ríoghachta Éireann" (Annals of the kingdom of Ireland) but now better known as the "Annals of the Four Masters". The 'four masters' in question are Mícheál Ó Cléirigh, Cú Choigcríche Ó Cléirigh, Fearfeasa Ó Maol Chonaire and Peregrine Ó Duibhgeannain and the term was devised by John Colgan. However, other important collaborators included Muiris mac Torna Uí Mhaolchonaire Ó Cléirigh's brother Conaire. The work was completed in August 1636 and two manuscript copies of the annals were made. He had an interest in Irish Lexicography and compiled a famous glossary called ‘Sanasán Mhichíl Uí Chléirigh’ (Michael O’Clery's Glossary). This glossary was printed in 1643 during the author's lifetime. These two glossaries and others are valuable for the etymological and encyclopaedic information contained in them.