The Collaborative International Dictionary of English v.0.48:

Seraphim \Ser"a*phim\, n.
   The Hebrew plural of Seraph. Cf. Cherubim.
   [1913 Webster]

   Note: The double plural form seraphims is sometimes used, as
         in the King James version of the Bible, --Isa. vi. 2
         and 6.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Seraph \Ser"aph\, n.; pl. E. Seraphs, Heb. Seraphim. [Heb.
   ser[=a]phim, pl.]
   One of an order of celestial beings, each having three pairs
   of wings. In ecclesiastical art and in poetry, a seraph is
   represented as one of a class of angels. --Isa. vi. 2.
   [1913 Webster]

         As full, as perfect, in vile man that mourns,
         As the rapt seraph that adores and burns. --Pope.
   [1913 Webster]

   Seraph moth (Zool.), any one of numerous species of
      geometrid moths of the genus Lobophora, having the hind
      wings deeply bilobed, so that they seem to have six wings.
      [1913 Webster] Seraphic

Moby Thesaurus II by Grady Ward, 1.0:

28 Moby Thesaurus words for "seraphim":
   angel, angel of light, angel of love, angelology, angels,
   archangel, archangels, beatified soul, canonized mortal, celestial,
   cherub, cherubim, dominations, dominions, heavenly being, martyr,
   messenger of God, patron saint, powers, principalities,
   principality, recording angel, saint, saved soul, seraph,
   soul in glory, thrones, virtues



Easton's 1897 Bible Dictionary:

Seraphim
   mentioned in Isa. 6:2, 3, 6, 7. This word means fiery ones, in
   allusion, as is supposed, to their burning love. They are
   represented as "standing" above the King as he sat upon his
   throne, ready at once to minister unto him. Their form appears
   to have been human, with the addition of wings. (See ANGELS.) This word, in the original, is used elsewhere only
   of the "fiery serpents" (Num. 21:6, 8; Deut. 8:15; comp. Isa.
   14:29; 30:6) sent by God as his instruments to inflict on the
   people the righteous penalty of sin.


Hitchcock's Bible Names Dictionary (late 1800's):

Seraphim, burning; fiery