big top is a noun meaning "a canvas tent to house the audience at a circus performance". It carries one recorded sense.
a canvas tent to house the audience at a circus performance
“he was afraid of a fire in the circus tent”
“they had the big top up in less than an hour”
Definitions, synonyms and semantic relations for big top come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.