https://doi.org/10.1351/goldbook.C01421
A molecular entity comprising a monocyclic ligand assembly that contains three or more binding sites held together by covalent bonds and capable of binding a guest in a central (or nearly central) position. The adducts formed are sometimes known as 'coronates'. The best known members of this group are macrocyclic polyethers, such as '18-crown-6', containing several repeating units –CR2–CR2O– (where R is most commonly H), and known as crown ethers. 
See also: host (in biotechnology)