Definition of thulium in US English:



  • The chemical element of atomic number 69, a soft silvery-white metal of the lanthanide series.

    • ‘The thulium material never recovers from the upwards resistive change, and continues recovery to the normal state as the compound is further cooled.’
    • ‘The main rare-earth ions used are thulium (for devices operating at 1450 to 1510 nm) and erbium.’
    • ‘The pure metal can be produced by treating thulium fluoride with calcium metal.’
    • ‘Each segment contains small amounts of ions of relatively rare metals, such as dysprosium, thulium, and cerium, which fluoresce in different colors.’
    • ‘The American chemist C. James performed 15,000 recrystallizations before pure thulium bromate was obtained.’


Late 19th century: modern Latin, from Latin Thule (see Thule (sense 1)), from Greek Thoulē, of unknown origin.