Possible Clues:

• Fully aware of
• "... ___ a midnight dreary ..."
• Part of many British place names
• '___ a slitted sheet I sit' (tongue twister phrase)
• ''Once --- a Mattress''
• ''Once ____ a midnight dreary''
• Onto
• ".. ___ a midnight dreary22
• "Once --- a time..."
• "___ a slitted sheet I sit" (tongue twister phrase)