the.com/rad

Peaked in 1989, never left, now ironic and sincere at once.

means Slang for excellent or cool — short, punchy, and built for enthusiastic agreement.

from A clipped form of 'radical,' which surfers and skaters started using in the 1970s–80s to mean extreme or awesome, then shortened further because saying three whole syllables wasn't very rad of you.

actual unit
radiation absorbed dose, 100 ergs per gram
slang debut
surfer and skater slang by the 1980s
linguistic trick
a palindrome that also means awesome backwards
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