• WordNet 3.6
    • n subkingdom (biology) a taxonomic group comprising a major division of a kingdom
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Webster's Revised Unabridged Dictionary
    • n Subkingdom One of the several primary divisions of either the animal, or vegetable kingdom, as, in zoölogy, the Vertebrata, Tunicata, Mollusca, Articulata, Molluscoidea, Echinodermata, Cœlentera, and the Protozoa; in botany, the Phanerogamia, and the Cryptogamia.
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Century Dictionary and Cyclopedia
    • n subkingdom A prime subdivision of the animal kingdom; a superclass corresponding to the “branches” or “embranchements” of French zoölogists, as Cuvier, who recognized the four subkingdoms of the vertebrates, mollusks, articulates, and radiates. Such main groups are now more commonly called phyla. Eight such groups now very generally recognized, in fact if not in name, are Protozoa, Cœlentera, Echinodermata, Vermes, Arthropoda, Molluscoidea, Mollusca, and Vertebrata. Some authors degrade Vermes from this rank, or otherwise dispose of it as a subkingdom; some elevate the Tunicata to this rank; and the Molluscoidea are not recognized by all as a subkingdoni.
    • n subkingdom In botany, a primary division of the vegetable kingdom; the highest class below the kingdom itself. The ordinary division is into two such subkingdoms, the Phanerogamia and the Cryptogamia; but late systematists incline to recognize four: Spermophyta (corresponding to the Phanerogamia), Pteridophyta, Bryophyta, and Thallophyta (corresponding to Cryptogamia).
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Chambers's Twentieth Century Dictionary
    • n Subkingdom sub-king′dum a subordinate kingdom: a division of a kingdom: a subdivision.
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In literature:

The "hundreds" make up the province or subkingdom.
"The Danish History, Books I-IX" by Saxo Grammaticus ("Saxo the Learned")
He divided animals into four great subkingdoms: Vertebrates, Mollusca, Articulata, Radiata.
"Thomas Henry Huxley; A Sketch Of His Life And Work" by P. Chalmers Mitchell