Lanthanum (element)
鑭 refers specifically to the chemical element lanthanum, a rare-earth metal. It has no extended everyday meanings beyond this technical sense.
鑭 is a modern character created for the element lanthanum. It combines the metal radical 金 with the phonetic component 闌 (ラン), following the typical pattern for chemical element names.
The left side 金 (metal) tells you it's a metallic element. The right side 闌 suggests the reading and helps identify it as lanthanum, a rare-earth metal.
For ラン, the right-side component 闌 itself is read ラン, so the kanji's reading is directly built in: 闌 -> ラン.