It was neither. Portmanteau is the word most often used, but the word I found was similar to conflation. I think 'conflation' was one of the words found en route to the word I'm trying to recall. I basically searched the dictionary - one word leading me onto another - until I came upon it. What really tickled me was that the word itself was a combination of two words, each of which described the process. I love when stuff like that happens!