旦 dàn
“dawn; morning; day”
On its own, an ordinary character; Cantonese daan3. Readings and gloss from the Unicode Unihan database.
Carries Tantalum
Transliterates syllable 1 of tan·ta·lum: tantalum → tǎn.
The reading drifted: the component is read dàn, the element tǎn.