Sentence:  <WSD>Tweedledum'</WSD>s chum stood with his hand resting lightly on the back of her arm, as if to turn her away from some potentially corrupting sight. [...] I stood my ground, smiled, and introduced myself. "I'm looking for Timothy Butler. That must be you." [...] I calmed down enough to notice that Timothy Butler was clenching and unclenching his right hand in an effort at self-control. <WSD>Tweedledum</WSD> noticed it too. She rushed to his defense. 
Meaning of the word marked with <WSD> tags:  One of a pair (the other of the pair being "Tweedle-dee") of nominally different (often: but practically identical) things.