An antonym for matter is anti-matter.
Anti-Federalist
anti-levee
anti-dote.
anti-threshold
A semitism
anti-federalists.
anti-perspirant
Anti member or exile
from the Greek prefix anti andonym as in synonym
The concept of "antonym" is used for properties, not for objects (or, in grammatical terms, for adjectives and adverbs, not for nouns). There is a particle called an "anti-neutron", but that can hardly be considered an antonym.
from the Greek prefix anti andonym as in synonym