reallocation vs apportionment

reallocation and apportionment both are nouns.

Word	Noun	Adjective	Verb	Adverb
reallocation	Yes	No	No	No
apportionment	Yes	No	No	No

As nouns, apportionment is a hypernym of reallocation; that is, apportionment is a word with a broader meaning than reallocation:

reallocation: a new apportionment (especially a new apportionment of congressional seats in the United States on the basis of census results)
apportionment: the act of distributing by allotting or apportioning; distribution according to a plan

Other hypernyms of reallocation include allocation, allotment, apportioning, assignation, parceling, parcelling.

reallocation (noun)	apportionment (noun)
a new apportionment (especially a new apportionment of congressional seats in the United States on the basis of census results)	the act of distributing by allotting or apportioning; distribution according to a plan
a share that has been allocated again