An appendage or extremity was an anatomical term collectively used to describe the head, tail, or limbs of a lifeform. In addition, these terms also described tentacles, wings, arms, hands, legs, feet, and ears.
When Enterprise NX-01 took aboard an unidentified symbiotic lifeform in late 2151, Malcolm Reed attempted to create a force field to repel it, without killing it, with a calculated jolt. When Doctor Phlox said he could not allow him to "pummel this appendage with EM radiation until it cries for mercy" because he determined that it was "more than just a severed limb", but in fact, it exhibited "all the signs of an intelligent being." (ENT: "Vox Sola")
Tucker with a cloaked appendage
The following year, Trip Tucker's arm was partially cloaked while working on a Suliban cell ship, he went to Dr. Phlox for advice. Phlox guessed that Tucker received "an intense dose of whatever particle radiation that ship uses to conceal itself." When Tucker feared that the condition might be permanent, Phlox told him "[i]t's difficult to determine, but I suspect your appendage will eventually re-materialize on its own." (ENT: "The Communicator")
Early internal symptoms of virus created as a result of the life prolongation project, included an intense fever, great pain in the extremities, fuzziness of vision. (TOS: "Miri")
Apollo's giant green hand
When the USS Enterprise was gripped by Apollo's giant green hand while in orbit of Pollux IV in 2267, Spock explained that "[d]espite its appearance, that of a Human appendage, it is definitely not living tissue. It is energy." (TOS: "Who Mourns for Adonais?")
When Riley Frazier and Orum revealed to Chakotay the release of Borg identities prior to 2373, they regained many of their original characteristics, such the sounds of their own voices, forgotten memories, their taste of food, as well as the return of their original skin pigmentation, and the ability to remove their Borg appendages. (VOY: "Unity")
In a deleted scene from ENT: "Broken Bow", Hoshi Sato asked Malcolm Reed what the symptoms of frostbite were. He told her "your appendages blister, peel and turn gangrenous."