DAY-GLO Meaning of DAY-GLO in English Day-Glo /ˈdeɪɡləʊ $ -ɡloʊ/ BrE AmE adjective trademark having a very bright orange, green, yellow, or pink colour:Day-Glo orange posters Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012