The Collaborative International Dictionary of English v.0.48:

Choker \Chok"er\, n.
   1. One who, or that which, chokes.
      [1913 Webster]

   2. A stiff wide cravat; a stock. [Slang]
      [1913 Webster]

WordNet (r) 3.0 (2006):

choker
    n 1: someone who kills by strangling [syn: garroter,
         garrotter, strangler, throttler, choker]
    2: an unfortunate person who is unable to perform effectively
       because of nervous tension or agitation; "he could win if he
       wasn't a choker"
    3: necklace that fits tightly around a woman's neck [syn:
       choker, collar, dog collar, neckband]
    4: a high tight collar [syn: choker, ruff, ruffle, neck
       ruff]