Just had a thought- checked 1910 Ulster Directory and found:
William Adair, Duke St., Waterside listed under Agricultural Implement Agents, Boot & Shoe Makers, emigration Agents, Seed & Manure Merchants.
William Adair, Waterside (may be same as above) listed under Leather & Hide Merchants.
William Adair & Son, Bishop St.: Posting Establishments, Herse Proprietors.