This is a crossword in which each word can be spelled uniquely as a series of chemical element symbols (elements are clued by the title, "Fusion"). Symbols are taken from the most recent IUPAC nomenclature, also available at WebElements.
The completed grid is given below.
| W | At | Er | Dy | Ne | Re | Ba | Te | He | Pt | Ar | C | H |
| As | I | O | K | At | Ag | Am | ||||||
| P | I | K | Er | Au | B | U | Rn | H | Al | O | Ge | N |
| C | At | Ti | La | Er | Rn | U | ||||||
| He | B | Re | W | Sm | I | Th | Er | S | V | I | Xe | N |
| Mo | Y | Ca | I | La | Tc | P | ||||||
| S | O | U | Nd | Pr | O | O | F | V | Al | H | Al | La |
| Y | I | I | U | S | Y | Te | ||||||
| N | At | Ce | N | C | H | Ru | S | Ca | P | I | Ta | N |
| Th | Be | I | Ac | Re | Ra | Ca | ||||||
| Es | Ca | Rg | At | O | I | Re | S | Cr | O | F | U | La |
| I | Re | U | F | O | Al | I | ||||||
| S | Ir | I | U | S | F | I | Re | W | Al | K | Er | S |
Once the grid is complete, "fuse" the elements from squares of the same color — find the chemical element whose atomic number is the sum of the atomic numbers of those elements.
| O | + | F | = | Cl | H | + | B | = | C | O | + | Dy | = | W | He | + | Be | = | C | S | + | Te | = | Er | ||||||
| H | + | N | = | O | C | + | Al | = | K | V | + | Sm | = | At | H | = | H | O | + | O | = | S |
When placed in the order of the color bar below the grid, these give the following:
| Cl | O | C | K | W | At | C | H | Er | S |
The answer is CLOCKWATCHERS.
2006 MIT Mystery Hunt