[1] : The Collaborative International Dictionary of English v.0.48

packet \pack"et\ pa^k"e^t, n. f. paquet, dim. fr. ll.
   paccus, from the same source as e. pack. see pack.
   1913 webster
   1. a small pack or package; a little bundle or parcel; as, a
      packet of letters. --shak.
      1913 webster

   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.
      1913 webster

   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.
      1913 webster
see also:
pack packet boat packet ship packet vessel packet packet day 
packet note packet post paper 

[2] : WordNet (r) 2.0

packet boat
     n : a boat for carrying mail syn: mailboat, mail boat, packet
see also:
mailboat mail boat packet 

[3] : Moby Thesaurus II by Grady Ward, 1.0

19 moby thesaurus words for "packet boat":
   carrier, carrier pigeon, homer, homing pigeon, mail car,
   mail coach, mail packet, mail train, mail truck, mailer, mailplane,
   pigeon post, post boat, post car, post coach, post-horse,
   post-office car, poster, railway mail car

Packet Boat >> P Words
Packet Boat, definition of term: Packet Boat
packet+boat_pag1.html

Boat >> B Words
Boat, definition of term: Boat
boat_pag1.html

Packet >> P Words
Packet, definition of term: Packet
packet_pag1.html

Packet Switchin >> P Words
Packet Switchin, definition of term: Packet Switchin
packet+switchin_pag1.html

Packet Radio >> P Words
Packet Radio, definition of term: Packet Radio
packet+radio_pag1.html

Pilot Boat >> P Words
Pilot Boat, definition of term: Pilot Boat
pilot+boat_pag1.html

Peter Boat >> P Words
Peter Boat, definition of term: Peter Boat
peter+boat_pag1.html

Patrol Boat >> P Words
Patrol Boat, definition of term: Patrol Boat
patrol+boat_pag1.html