THIS is a fascinating compilation of words and phrases that have "filtered from Irish into the English of Ireland", collected in Diarmaid O Muirithe's lifetime in "places where Irish had long since died". This word-hoard has enriched Anglo-Irish - a term which will not please everyone, as O Muirithe readily concedes - so that the language spoken in Ireland still has something of the tang and vividness of Elizabethan English. Yet it is also a testament to the social disasters of the Irish 19th century, which brought about the final loss of Gaelic as the national tongue. Paradoxically, that loss entailed a very great gain, for the Anglo-Irish, or Hiberno-English, which resulted from it proved to be an invaluable literary medium in the hands of Synge, Yeats, Joyce, Beckett, and is still in use even among the younger, urban novelists such as Roddy Doyle, Dermot Bolger, Anne Enright. "Indispensable" is a much abused word, but in the case of this dictionary its use is fully justified.