Entry 1 sense Webster, 1913 Haemacyanin /(-sī"ȧ*nĭn)/ · Haem·a·cy·a·nin · IPA 01 n. A substance found in the blood of the octopus, which gives to it its blue color. 1. A substance found in the blood of the octopus, which gives to it its blue color.(Physiol. Chem.)