No. Compound is not a compound word because if you try to separate it, you would get com & pound. Com is not a word (the com in a website does not qualify as a word).
The Hebrew translation for 'brother-in-law' is GIS גיס.
One compound word is windshield.
The origin of the word because is: by cause, so yes it could be called a compound word.
underarm underage underbelly underbrush undercoat underclass underclothes undercover underdog underground undergrowth undergone underhand underline underlie undermine underpass underpin underplay...