What is "packet day"

packet \pack"et\ (p[a^]k"[e^]t), n. [F. paquet, dim. fr. LL. paccus, from the same source as E. pack. See Pack.]

1. A small pack or package; a little bundle or parcel; as, a packet of letters.
   --Shak.

2. Originally, a vessel employed by government to convey dispatches or mails; hence, a vessel employed in conveying dispatches, mails, passengers, and goods, and having fixed days of sailing; a mail boat.

   Packet boat, Packet ship, or Packet vessel. See Packet, n., 2.

   Packet day, the day for mailing letters to go by packet; or the sailing day.

   Packet note or Packet post. See under Paper.