terms for words

[Sam Clements]

What is the technical name for a word such as "gaydar?"

Also, for a word that is formed from the first syllable of two words, is there a technical name?  Is this still a portmanteau?  And, what's the earliest word of this type?

I assume that portmanteau is the technical name for taking the first syllable of one word and the final syllable of another and combing them to form a new word, such as motel.  I know that this word form goes back to at least Lewis Carrol.