If you pick up a dictionary of moderate size, you will find at least ten or twelve completely different meanings. Two completely different and dissimilar things cannot come together. Only two things which are basically and fundamentally identical can ever become one. If these unions were between two completely and dissimilar things, they could never come together.
Yoga is the unity, or the harmony, or the oneness, that exists already.
If we avoid placing emphasis on what appears to be the dissimilarities, we won't have to battle to become one. Unless you understand this also, you cannot realize oneness. The easiest way to understand this is to use the example of a blackboard. Where you have written that word is the only place where the blackness or the omnipresence does not seem to exist. You can wipe off the white chalk and the blackboard is black one again, because the blackness was there all the time.