There is no dictionary entry for the word "unsupplest." It seems to be a non-standard word as it does not appear in reputable dictionaries, word lists, or language references. However, based on its structure and prefixes, one can infer a hypothetical definition.
The prefix "un-" often denotes negation or reversal, implying the opposite meaning of a word. Similarly, the suffix "-est" signifies the superlative form of an adjective. So, combining these elements, "unsupplest" could be interpreted as the strongest or most extreme form of lacking suppleness or flexibility, emphasizing an absolute lack of limberness or adaptability.
Suppleness, in a general sense, refers to the quality of being flexible, adaptable, or easily bent without breaking. It can pertain to physical objects, such as materials, or be used metaphorically to describe people, attitudes, or situations that can accommodate change or are responsive to new ideas. Therefore, "unsupplest" might suggest an entity or condition that is entirely devoid of any ability to yield, adjust, or adapt.
However, it is important to note that due to the nonexistence of "unsupplest" in standard usage, this definition is only a speculative interpretation.
