Possible Clues:

• Ref. work
• Ref. book
• Desk ref. book
• Wordsmith's ref.
• Webster's, e.g.: Abbr.
• Webster's, e.g.: Abbr
• Wds. are defined in it
• Merriam-Webster ref
• Crossworder's crutch: Abbr.
• The OED, e.g.