Webster's 1913 Dictionary
THALLUS
Thal "lus, n.; pl. Thalli. Etym: [NL. , fr. Gr. (Bot. )
Defn: A solid mass of cellular tissue, consisting of one or more layers, usually in the form of a flat stratum or expansion, but sometimes erect or pendulous, and elongated and branching, and forming the substance of the thallogens.
New American Oxford Dictionary
thallus
thal lus |ˈTHaləs ˈθæləs | ▶noun ( pl. thalli |ˈTHalī | ) Botany a plant body that is not differentiated into stem and leaves and lacks true roots and a vascular system. Thalli are typical of algae, fungi, lichens, and some liverworts. DERIVATIVES thal loid |ˈTHaloid |adjective ORIGIN early 19th cent.: from Greek thallos ‘green shoot, ’ from thallein ‘to bloom. ’
Oxford Dictionary
thallus
thallus |ˈθaləs | ▶noun ( pl. thalli |-lʌɪ, -liː | ) Botany a plant body that is not differentiated into stem and leaves and lacks true roots and a vascular system. Thalli are typical of algae, fungi, lichens, and some liverworts. DERIVATIVES thalloid adjective ORIGIN early 19th cent.: from Greek thallos ‘green shoot ’, from thallein ‘to bloom ’.
Duden Dictionary
Thallus
Thal lus Substantiv, maskulin , der |Th a llus |der Thallus; Genitiv: des Thallus, Plural: die Thalli griechisch-lateinisch primitiver Pflanzenkörper der Thallophyten (ohne Wurzeln und Blätter ); Gegensatz Kormus
The Wordsmith Dictionary