WordNet records no synonym and no antonym for calender. 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 machine that smooths or glazes paper or cloth by pressing it between plates or passing it through rollers
press between rollers or plates so as to smooth, glaze, or thin into sheets
“calender paper”
Synonyms, antonyms and the broader and narrower relations for calender come from Princeton University’s WordNet. Full sources and licences.