The Collaborative International Dictionary of English v.0.48:
Contortionist \Con*tor"tion*ist\ (k[o^]n*t[^o]"sh[u^]n*[i^]st), n. One who makes or practices contortions; especially, a gymnast who is able to twist the limbs into positions impossible for normal people to achieve. [1913 Webster +PJC]WordNet (r) 3.0 (2006):
contortionist n 1: an acrobat able to twist into unusual positions