Tm rare uk noun 1. 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 Synonymsthuliumatomic number 69 Related words Broader terms metallic element Parts apatitemonazitexenotime WordNet 2.1 (Princeton University). WordNet 2.1 Copyright Princeton University. All rights reserved.
