adj. Pertaining to or containing the element thallium, especially with valence 3.
adj. Pertaining to a thallus.
the GNU version of the Collaborative International Dictionary of English
adj. Of or pertaining to thallium; derived from, or containing, thallium; specifically, designating those compounds in which the element has a higher valence as contrasted with the thallous compounds.
The Century Dictionary and Cyclopedia
In chem., of, pertaining to, or containing thallium: as, thallic acid.