WordNet records no synonym and no antonym for soldier. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
an enlisted man or woman who serves in an army
“the soldiers stood at attention”
Synonyms, antonyms and the broader and narrower relations for soldier come from Princeton University’s WordNet. Full sources and licences.
a wingless sterile ant or termite having a large head and powerful jaws adapted for defending the colony