Is a lien and a caveat the same thing?

No, a 'lien' is a claim against some sort of asset, where what ever that is, where one has standing. An asset is defined, like just about everything else, by the jurisdiction. It mainly means, something that has some worth and is more or less not changing but by the market place valuation. (In today's market that means about ever 15 minutes or so.) On the other hand a 'caveat' is a very old legal Word which more or less means that a formal statment has been made to a court, which demands that the court hold off on what it's been doing until the questions which have been raised get answered by a 'hearing' before the court. The term generally arrises in probate court and deals generally with wills and estates and such in the courts which deal with 'estates' and such. (one says 'such' because many states dont really reconize the esistance of 'estates' as legal entities. It's a shorthand Word to describe a bunch of stuff to a court which asserts that something needs to be held off on until a diffierent opinion can be considered in a formal proceeding.