Definitions
American Heritage® Dictionary of the English Language, Fourth Edition
- n. A word formed by merging the sounds and meanings of two different words, as chortle, from chuckle and snort.
Wiktionary
- n. A word which combines the meaning of two words (or, rarely, more than two words), formed by combining the words, usually, but not always, by adjoining the first part of one word and the last part of the other, the adjoining parts often having a common vowel; for example, smog, formed from smoke and fog.
WordNet 3.0
- n. a new word formed by joining two others and combining their meanings
Examples
“Daisy was to be the Prioress – because she is good, and has "a soft little red mouth," and H.O. would be the Manciple (I don't know what that is), because the picture of him is bigger than most of the others, and he said Manciple was a nice portmanteau word – half mandarin and half disciple.”
Lists
These user-created lists contain the word ‘portmanteau word’.

seanahan See portmanteau, or the tag for portmanteau. May 27, 2008
oroboros A word formed by mixing two other words: brunch from breakfast and lunch. May 23, 2008