That would be a hard 'th' (dh) wouldn't it? As in 'the' not as in 'thing.'
It is borrowing, whether or not it means the same thing. And in this case it does mean pretty much the same thing anyway.
English borrows any word from any language that it thinks it can use in any way it sees fit. That's the genius of the language! We English speakers never let meaning get in the way of stealing a nice word. And even when it does mean exactly the same thing at the time it is borrowed, give it a generation or two and it will go the same way as other English words - its meaning will drift and/or expand with usage. Other Spanish loan words that have come to be used in ways other than their original meaning or context would include gusto, taco, gringo, and probably most other words ending in 'o'
