vesica piscis
Concise Oxford English Dictionary © 2008 Oxford University Press:
vesica piscis /ˌvɛsɪkə ˈpɪskɪs, ˈviː-/
▶noun (pl. vesicae piscis /ˈvɛsɪkiː, ˈviː-/) a pointed oval shape used as an architectural feature and as an aureole enclosing figures such as Christ or the Virgin Mary in medieval art.
– origin L., lit. ‘fish's bladder’.
'vesica piscis' also found in these Oxford entries:

