The uppermost part of something is the part that is higher than the rest of it. The uppermost thing is the highest one of a group of things. John was on the uppermost floor of the three-storey gatehouse The rain spattered on the uppermost leaves. = topmost Uppermost is also an adverb. Lift the fish and carefully place it on a large board, flat side uppermost. = up
If something is uppermost in a particular situation, it is the most important thing in that situation. The economy appears to be uppermost in people's minds