Merriam-Webster Collegiate Dictionary - thallus

 noun  (plural thalli or ~es)  Etymology: New Latin, from Greek thallos, from thallein to sprout; akin to Armenian dalar green, fresh, Albanian dal I come forth  Date: 1829 a plant body that lacks differentiation into distinct members (as stem, leaves, and roots), does not grow from an apical point, and is characteristic of organisms formerly classified as thallophytes THAMES  geographical name  1. river 15 miles (24 kilometers) SE Connecticut, an estuary flowing S into Long Island Sound  2. river 135 miles (217 kilometers) Canada in SE Ontario flowing S & SW into Lake St. Clair  3. river over 200 miles (322 kilometers) S England flowing from the Cotswolds in Gloucestershire E into the North Sea — see Isis