WordNet records no synonym and no antonym for dotted line. It is the only member of its synset, 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 line made up of dots or dashes; often used to indicate where you are supposed to sign a contract
“just sign on the dotted line”
Synonyms, antonyms and the broader and narrower relations for dotted line come from Princeton University’s WordNet. Full sources and licences.