The Collaborative International Dictionary of English v.0.48:
Synteresis \Syn`te*re"sis\, n. [NL., fr. Gr. ? preservation, fr. ? to preserve; sy`n with + ? to guard.] 1. (Med.) Prophylaxis. [Obs.] [1913 Webster] 2. (Metaph.) Conscience viewed as the internal repository of the laws of duty. --Whewell. [1913 Webster]