Arm

An arm was a body part.

By number
The Tenth Doctor thought it would be "brilliant" to have four arms, as he could do everything he normally did with only two of them, and still have a pair of arms free for some knitting. (AUDIO: Infamy of the Zaross)

Decoration
Vislor Turlough and his brother Malkon each had the Misos Triangle branded on an arm. (TV: Planet of Fire)

A way that some people reminded themselves that they had encountered the Silence was to make tally marks on their arms. (TV: Day of the Moon)

Individual cases
According to Faction Paradox legend, Grandfather Paradox had only one arm. (PROSE: The Gallifrey Chronicles) A future version of the Eighth Doctor whose biodata had been corrupted by the Faction modelled himself as Grandfather Paradox, including removing one of his arms. This also may have been because he knew it was the arm which the Doctor would use to destroy Gallifrey. (PROSE: The Ancestor Cell)

The Ninth Doctor pulled off the plastic arm of an Auton when it came between the doors of a lift he and Rose Tyler were using to escape them in Henrik's. Left with the arm, Rose took it back home to the Powell Estate where it was picked up and thrown in the bin by Mickey Smith. On the following day, it was animated by the Nestene Consciousness and, making its way back through the cat flap, proceeded to attack the Doctor then Rose before the Doctor used the sonic screwdriver to sever the Nestene signal, rendering it "armless". He found that the arm was too "simple" to be used to trace the Nestene Consciousness. (TV: Rose)

In 2012, Rose Tyler and the Ninth Doctor found the arm of a Raxacoricofallapatorian in Henry van Statten's vault. Believing it to be of a Slitheen, Rose observed that it had been stuffed. (TV: Dalek)

Immediately following his regeneration, the Tenth Doctor made sure to check that he still had, among other things, two arms. (TV: Born Again)

The Abzorbaloff had hands with three clawed fingers, which exposed him as alien to Ursula Blake and Elton Pope when he attempted to hide behind a copy of The Daily Telegraph newspaper. Ursula was absorbed into the Abzorbaloff's body when his hand grabbed her arm. (TV: Love & Monsters)

The Eleventh Doctor and Amy Pond were attacked by a "Cyber-arm" in the underhenge. (TV: The Pandorica Opens)

Auntie had the Corsair's left arm grafted onto her by House. (TV: The Doctor's Wife)