combination vs fusion

combination and fusion both are nouns.

Word	Noun	Adjective	Verb	Adverb
combination	Yes	No	No	No
fusion	Yes	No	No	No

As nouns, fusion is a hyponym of combination; that is, fusion is a word with a more specific, narrower meaning than combination:

combination (noun)	fusion (noun)
the act of combining things to form a new whole	the act of fusing (or melting) together
the act of arranging elements into specified groups without regard to order	correction of an unstable part of the spine by joining two or more vertebrae; usually done surgically but sometimes done by traction or immobilization
a collection of things that have been combined; an assemblage of separate parts or qualities	the combining of images from the two eyes to form a single visual percept
a group of people (often temporary) having a common purpose	an occurrence that involves the production of a union
a sequence of numbers or letters that opens a combination lock	a nuclear reaction in which nuclei combine to form more massive nuclei with the simultaneous release of energy
an alliance of people or corporations or countries for a special purpose (formerly to achieve some antisocial end but now for general political or economic purposes)	the merging of adjacent sounds or syllables or words
a coordinated sequence of chess moves	the state of being combined into one body