sinki

The seam here is the best-disguised one in the band, and it is entirely false. Sin is a word - the accusative of the reflexive si, oneself, and one of the commonest short words in the language. So sinki looks like sin plus a verb ending, some sort of self-directed action. It is not. Sink- is one root, borrowed whole from Germanic, and the sin you can see is the first three letters of a five-letter word. Compare sinki with sin kaŝi, to hide oneself: same three letters, an entirely different piece of grammar, and a space in the middle of one of them.

It is intransitive, and that is the fact to hold. A thing sinkas by itself. To sink something else you need sinkigi, with the -ig- causative: la ŝtormo sinkigis la ŝipon, the storm sank the ship. Getting this the wrong way round is the single commonest verb error in Esperanto and it has nothing to do with vocabulary - see the transitivity article, which is about exactly this.

Against droni. Droni is what happens to a person or an animal in water: to drown. Sinki is what happens to anything that goes downwards through a medium, and it needs neither water nor a victim - the sun sinkas behind the hills, prices sinkas, a heart sinkas. A person who sinkas is going under; a person who dronas is dying.