WordNet records no synonym and no antonym for clear and present danger. 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 standard for judging when freedom of speech can be abridged
“no one has a right to shout `fire' in a crowded theater when there is no fire because such an action would pose a clear and present danger to public safety”
Synonyms, antonyms and the broader and narrower relations for clear and present danger come from Princeton University’s WordNet. Full sources and licences.