dilatation
Concise Oxford English Dictionary © 2008 Oxford University Press:
dilatation /ˌdʌɪleɪˈteɪʃ(ə)n, ˌdɪ-, -lə-/
▶noun chiefly Medicine & Physiology the action of dilating a vessel or opening or the process of becoming dilated.
■ a dilated part of a hollow organ or vessel.
'dilatation' also found in these Oxford entries:

