From ZooTerms (Dictionary of Invertebrate Zoology)
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arm (noun; Anglo-Saxon arm, forelimb): 1. Anything resembling or corresponding to an arm.

2. (Echinodermata) a. In Asteroidea, the radial extension of the body surrounding the axis; the ambulacra. b. In Crinoidea, the radial evagination of the body extending from the theca; undivided distal branches.

3. (Echiura) The forked section of the proboscis.

4. (Mollusca: Cephalopoda) a. In squids and cuttlefish, eight of the ten short and heavy appendages around the head, the other two larger dorsal appendages being tentacles. b. The tentacles of an octopod.