The Collaborative International Dictionary of English v.0.48:
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.