The word "doeth thoroughly" is an archaic form of English which is rarely used nowadays. It is spelled as /dʌθ ˈθʌrəli/ in the International Phonetic Alphabet. The spelling is a combination of the verb "doeth", which is the third-person singular present tense form of "do" in Early Modern English, and the adverb "thoroughly". The word is found in older literature and documents, such as the King James Bible. Today, we commonly use the simpler and more modern spelling of "does thoroughly" to convey the same meaning.
The phrase "doeth thoroughly" is composed of two words: "doeth" and "thoroughly".
1. "Doeth" is the third-person singular present tense of the verb "do" in Early Modern English. It comes from the Old English word "dōth" which means "does". Over time, the form "doeth" evolved as a variant of "doth" which was commonly used as a present tense marker in Early Modern English.
2. "Thoroughly" comes from the Middle English word "thuruh" which meant "through". It originated from the Old English word "þurh" with the same meaning. Over time, "þurh" evolved into the Middle English "thorough" meaning "fully", which eventually became "thoroughly".
When these two words are combined, "doeth thoroughly" means "does completely" or "acts fully".