1. Through - This word comes from the Old English "thuruh," meaning "through" or "across," which is closely related to the Old English "troh," the root of "trough."
2. Thorough - This word also comes from the Old English "thuruh," with the added suffix "-ough," emphasizing the completeness and intensity of going "through" something.
3. Thru - This is a shortened form of "through," often used in informal writing or speech, maintaining the core meaning of "through" or "across."