Meaning

adjective painstakingly careful and accurate

adjective performed comprehensively and completely

originFrom Middle English thoruȝ, þoruȝ, from Old English þuruh, a byform of Old English þurh, whence comes English through. The adjective derives from the preposition and adverb. The word developed a syllabic form in cases where the word was fully stressed: when it was used as an adverb, adjective, or noun, and less commonly when used as a preposition.

Etymology from Wiktionary, CC BY-SA 3.0