The sort of compound words which we're discussing appear by a process of synthesis:

https://en.wikipedia.org/wiki/Synthetic_language

See also: agglutination https://en.wikipedia.org/wiki/Agglutination

A portmanteau is different, where parts of several words are blended, rather than retaining the substance of each word in a compound.

https://en.wikipedia.org/wiki/Blend_word

And let's not forget xkcd's coinage of the malamanteau:

https://xkcd.com/739/