Use of "astra/o" as an ending on a relative

Question

Another one of my basic questions.

In English, I use step in front of just about any relative to make them a step-relative. In Spanish I have only seen hijastra/o, padrastro, madrastra, abuelastra/o. Is it legitimate to to extend the concept- eg tiastra/o or primastra/o or would it never be done.

Answer 1

I did a google search, and there seem to be regional differences. "-astro" does not appear to be used for "primo" or "tío".

The phrases that came up were "primo no consanguíneo" or "primo por parte de mi madrastra" (as an example).

Thanks- just trying to see how far I can push it- I can find a few nietrastra/o usages, but very few and couldn't find any of the others save one primastro that seemed to be a nickname rather than normal usage - Stadt, Oct 3, 2010