noun, noun which may take the genitive case particle 'no'
confidential; personal; to be opened only by addressee
Used on envelopes or documents to indicate that the contents are private and should be opened only by the named recipient.
The envelope is marked 'Confidential'.
I received a confidential letter.
confidential letter
registered mail to addressee in person; PD PR
From 親 (intimate, personal) and 展 (open, unfold), literally 'to open personally'. The exact historical derivation is uncertain, but the compound has been used in Japanese correspondence for many decades.