Thulium

Thulium is the rarest naturally occurring lanthanide element and is named after Thule, an ancient name for Scandinavia (or possibly a mythical northern land). Discovered in 1879 by Per Teodor Cleve, thulium is a silvery metal that is soft enough to cut with a knife. It took decades before scientists could produce it in pure form.

Despite its rarity, thulium has some important uses. Portable X-ray machines use thulium-170 as a radiation source — these devices are used by doctors in remote areas and by security personnel. Thulium-doped fiber lasers operate at wavelengths useful for military applications and medical procedures. Thulium is also used in euro banknote security features, similar to europium.

Thulium's symbol 'Tm' is a distinctive two-letter element in Spellement. While 'tm' is uncommon at word beginnings, partial emphasis lets spellers use 't' or 'm' individually. Both are among the most frequent consonants in English, making thulium a flexible building block for creative word spellings.