WordNet records no synonym and no antonym for railhead. 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.
a railroad depot in a theater of operations where military supplies are unloaded for distribution
the end of the completed track on an unfinished railway
Synonyms, antonyms and the broader and narrower relations for railhead come from Princeton University’s WordNet. Full sources and licences.