The Collaborative International Dictionary of English v.0.48:
externalisation \externalisation\ n. embodying in an outward form. Syn: externalization, exteriorization, exteriorisation. [WordNet 1.5]WordNet (r) 3.0 (2006):
externalisation n 1: attributing to outside causes [syn: externalization, externalisation] 2: embodying in an outward form [syn: externalization, externalisation, exteriorization, exteriorisation]