Related Clues:

• Imperceptible by the eye
• __ camera
• Writer of unseen words?
• Concealed from view
• Switch a cream pie when no one's looking
• Hard to put a name to home that's not obvious
• Obscure female, one with two daughters to accommodate
• Belief that ink might be this in thing?
• Cryptic crossword finally found in papers taken by woman
• Hidden, in Paris
• After end of lunch, I'd study out of sight
• Secret I'd discovered initially guarded by female
• Part of orchid denied or concealed
• Hidden delta in South American country
• 'Oh may I join the choir ____' (George Eliot, later borrowed by Monty Python)