Traditionally, not many useful Irish dictionaries have existed, and those that have existed - while being of highest quality - may not have been updated in decades. The world of the Internet (an Idirlíon) has given a new place for the Irish language to exist. Learners and speakers of Irish who may have been once isolated can now communicate online. Online Irish tools have also been developed.
Below I list the big Irish word reference sites that you can use for translations.
EnglishIrishDictionary.com is probably the most popular Irish English dictionary online. It’s quick to use, and contains most common-day entries. It seems to be based on the database of Collin’s Irish dictionaries. You can search quickly in both Irish and English.
Focal.ie is lead by Dublin City University, probably arising from their Irish-language entrepeneurship centre called Fiontar. Focal.ie is quite extensive, and contains many everyday words, but brands itself as a “terminology database” rather than a full dictionary. It is great for science and technology terms. Focal.ie has a bi-lingual interface, and you can search for terms in both English or Irish.
An Foclóir Beag is a dictionary hosted by the University of Limerick, and has an Irish-only interface. It is an Irish-Irish dictionary, and is especially useful for its verb tables.
Acmhainn.ie is another searchable Irish terminology resource. It’s an Irish-only interface, and classifies terminology for subjects such as biology, health and media.
An Chrannóg has a non-searchable word list, but has its 13,000 headwords classified by alphabetical letter.
Irish Gaelic Translator.com is not a dictionary, but a community-based translation forum. You can register on the forum and ask the community for Irish translations, and search existing translations. If the translation is uncertain, members will discuss what is the best translation for your phrase.
Let me know of any other online Irish dictionary!