The root word 'terminate' comes from the Latin 'terminare,' which means to limit or to end. In the context of the word 'interminable,' the prefix 'in-' negates the root, indicating the opposite. Therefore, 'interminable' describes something that cannot be terminated or brought to an end, hence it means endless or perpetual. This understanding of root words and prefixes is essential for deciphering the meanings of complex words in the English language.