No chronology of Old Norse loanwords in Irish has previously been proposed based on linguistic criteria, although much has been written on this subject for Latin loans in Irish. This study takes the first step in establishing a relative chronology of Old Norse loanwords based on sound changes in the recipient language, using existing knowledge about the history of Irish sound change. By comparing Old Norse loanwords found in Old and Middle Irish materials to their Old Norse source words, several divergences from the otherwise predictable process of phonological adaptation were identified. These variations can be linked to known sound changes in Irish during its contact with Old Norse, allowing us to establish different periods of borrowing for different loans. The study shows how, through linguistic analysis, we can uncover dating evidence and information about the contact situation that is not available to us from the historical record.