WordNet records no synonym and no antonym for lateral thinking. 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 heuristic for solving problems; you try to look at the problem from many angles instead of tackling it head-on
Synonyms, antonyms and the broader and narrower relations for lateral thinking come from Princeton University’s WordNet. Full sources and licences.