þurh [OE]
thurgh [MI]
through [ME]
þru
https://www.etymonline.com/word/through#etymonline_v_13275
https://www.merriam-webster.com/dictionary/through#dictionary-entry-1
https://quod.lib.umich.edu/m/middle-english-dictionary/dictionary/MED45600
https://bosworthtoller.com/32252