Meaning
Any form of an element having a different isotopic composition to that of the natural element, and thus a different atomic weight.
Etymology
Origin: Unknown
From allo- + bar. According to Alfred J. Henry, the meteorology sense was coined in Swedish by Nils Gustaf Ekholm.
NYT Puzzle Appearances
No published puzzle dates on file for this word yet. It is part of the official NYT Spelling Bee word list for 2019, 2020, 2021, 2024, 2025, 2026.