Definition
A radioactive chemical element, symbol At, atomic number 85. It is one of the rarest naturally occurring elements and belongs to the halogen group on the periodic table. All of its isotopes are unstable and decay quickly.
Plain English
A very rare, unstable element that breaks down into other elements over time. It appears in technical reference material but has no direct role in flying an aircraft.
Context Anchor
Most likely seen in chemical, hazardous-material, or reference material, not in normal cockpit procedures.
Derivation
From the Greek 'astatos,' meaning 'unstable.' The name reflects the element's defining property — it does not stay in one form for long before decaying.
Example Sentence 1
Astatine was listed in the dictionary's chemistry appendix alongside other halogen elements.
Example Sentence 2
Scientists study astatine in laboratories to understand radioactive decay patterns.