1 the act or an instance of fusing or melting.
2 a fused mass.
3 the blending of different things into one.
4 a coalition.
5 Physics = nuclear fusion.
Phrases and idioms:
fusion bomb a bomb involving nuclear fusion, esp. a hydrogen bomb.
Derivatives:
fusional adj.
Etymology: F fusion or L fusio (as FUSE(1))
Useful english dictionary. 2012.