No, it's not a root word. 'Simul' stems from the Latin meaning 'at the same time' and 'taneous' appears to be abstracted from 'spontaneous'. Neither of those are whole words in English, however, so the irreducible English word here is 'simultaneous.' The suffix 'ly' makes it an adverb.
Fugitive has no root word it is the root word.
There is no root word of river. It itself is a root word.
the root word is'confirminglyishness'
Root word is usual.
the root word is decor and that is the root word of decorate
The root word is gift.
end is the root word
Tri is the root word of intricate. The root word means three.
The root word of impersonal is person.
The root of the word unbreakable is break.
The root word for "combine" is "com-" which means "together" or "with".
the root word is vent