Much like Pure, the first book in Baggott's trilogy, Fuse has a deceptively simple title. It might be tempting to think "Oh, yes. Fuse. People are fused to things. Got it!"
But then you'd be missing half the meaning—and all of the cleverness—of this title.
We need to take the other titles of the trilogy into account as we analyze this title. The trilogy has the names Pure, Fuse, and Burn in that order — that's not just a coincidence. Sure, we deal with Pures in Fuse, burns in Pure, and fusings in Burn. In fact, all of these names (pure, fuse, burn) can be found in every book; but there's a reason why the first book is called Pure and not Fuse, (and vice versa).
Pure's main focus is on the struggle between the Dome and outside of the Dome, and, although there's an emphasis on the individual scars and suffering of characters, we mostly get the surface of their scars. But in Fuse, we dig much deeper into the individual fusings of each character—in particular, El Capitan and Helmud's fusing is vividly illuminated.
In Fuse, we also start to delve into the relationships of characters, highlighting emotional fusings. Pressia and Bradwell start to drift apart in the beginning, but then come close together by the end. Similarly, Lyda's pregnancy with Partridge can be seen as a literal fusing.
And then, of course, there's the wordplay present in the titles Fuse and Burn. A fuse is the string you light when you're planning on detonating a bomb: Fuse contains a little foreshadowing for the next installment in the trilogy. Things are literally about to heat up.