The Collaborative International Dictionary of English v.0.48:

Cephalopoda \Ceph`a*lop"o*da\ (s[e^]f`[.a]*l[o^]p"[-o]*d[.a]),
   n. pl. [NL., gr. Gr. kefalh` head + -poda: cf. F.
   c['e]phalopode.] (Zool.)
   The highest class of Mollusca.
   [1913 Webster]

   Note: They have, around the front of the head, a group of
         elongated muscular arms, which are usually furnished
         with prehensile suckers or hooks. The head is highly
         developed, with large, well organized eyes and ears,
         and usually with a cartilaginous brain case. The higher
         forms, as the cuttlefishes, squids, and octopi, swim
         rapidly by ejecting a jet of water from the tubular
         siphon beneath the head. They have a pair of powerful
         horny jaws shaped like a parrot's beak, and a bag of
         inklike fluid which they can eject from the siphon,
         thus clouding the water in order to escape from their
         enemies. They are divided into two orders, the
         Dibranchiata, having two gills and eight or ten
         sucker-bearing arms, and the Tetrabranchiata, with
         four gills and numerous arms without suckers. The
         latter are all extinct except the Nautilus. See
         Octopus, Squid, Nautilus.
         [1913 Webster] Cephalopodic

WordNet (r) 3.0 (2006):

Cephalopoda
    n 1: octopuses; squids; cuttlefish; pearly nautilus [syn:
         Cephalopoda, class Cephalopoda]