The Collaborative International Dictionary of English v.0.48:

hypertension \hypertension\ n.
   abnormally high blood pressure; especially, the chronic
   condition associated with persistent high blood pressure.
   [PJC]

WordNet (r) 3.0 (2006):

hypertension
    n 1: a common disorder in which blood pressure remains
         abnormally high (a reading of 140/90 mm Hg or greater)
         [syn: high blood pressure, hypertension] [ant:
         hypotension]