Cowardice was a trait associated with fear. One who displayed cowardice was refered to as a coward.

H. G. Wells told the Sixth Doctor that everyone at his school believed that he was a coward because he did not like cricket. (TV: Timelash)

"Metaltron", ostensibly the last Dalek in existence, branded the Ninth Doctor a coward, noting that he had survived after wiping out the Daleks and the Time Lords. (TV: Dalek)

Just prior to the Battle of the Game Station. Jack Harkness told the Ninth Doctor that he wished he had never met him, claiming that he was much better off as a coward.

Daring the Doctor to use a delta wave generator to wipe out his Dalek Fleet at the cost of all life on Earth, the Dalek Emperor asked him "What are you, coward or killer?" At the last moment, the Doctor relented using the delta wave, naming himself "coward. Any day." (TV: The Parting of the Ways)

Even at gunpoint, the Master correctly predicted that the Tenth Doctor could not kill him, branding him a coward. (TV: The End of Time)

The Eleventh Doctor made an observation to Gibbis, a native of Tivoli, regarding the cowardice of his people.

Your cowardice isn't quaint, it's sly, aggressive. It's how that gene of gutlessness has survived while so many others have perished.The Eleventh Doctor. [src]

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