large molecule

https://doi.org/10.1351/goldbook.12277
Molecule of size similar to or larger than the wavelength of the radiation in the solvent used.
Note: A molecule is treated as large if the length of its largest dimension exceeds about one-twentieth of the wavelength employed.
Source:
PAC, 2015, 87, 71. (Definitions of terms relating to individual macromolecules, macromolecular assemblies, polymer solutions, and amorphous bulk polymers (IUPAC Recommendations 2014)) on page 107 [Terms] [Paper]