The superlative form of 'flat'; having the least thickness, height, or dimensional projection compared to all other similar things.
From Old Norse 'flatr,' the root of English 'flat.' The superlative '-est' suffix (as in 'biggest,' 'smallest') indicates the extreme degree of the quality.
The word 'flat' is actually a relative newcomer to English (12th century from Scandinavia), while Romance languages have much older words for this concept—showing how English adopted words from different linguistic sources!
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