The term "Northern Irelander" generally refers to people from the region of Northern Ireland, which is part of the United Kingdom. If you are looking for synonyms for this term, there are a few options to consider. One option is to simply use the term "Irish" since people from Northern Ireland are technically Irish citizens. Another option is to use the term "Ulsterman" or "Ulsterwoman", which refers specifically to people from the province of Ulster, which includes Northern Ireland. Additionally, you could use the term "Northern Irish" or "Norn Iron" which are more colloquial terms used by locals. Ultimately, the term you choose will depend on the context and your specific audience.