Related Clues:

• Library gizmo
• One playing the field
• U-235 or C-14, e.g.
• Element form
• Post office gizmo
• Heavy hydrogen, e.g.
• Library device
• Office stamp
• Carbon 13 or cobalt 60
• Chemist's study
• Librarian's gadget
• Library stamp
• Time stamp
• Chemical relative
• Elemental form