Noun tm has 1 sense
  1. thulium, Tm, atomic number 69 - a soft silvery metallic element of the rare earth group; isotope 170 emits X-rays and is used in small portable X-ray machines; it occurs in monazite and apatite and xenotime
    --1 is a kind of metallic element, metal
    --1 is a substance of apatite; monazite; xenotime
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