Was
Old English bēon, an irregular and defective verb, whose full conjugation derives from several originally distinct verbs. The forms am and is are from an Indo-European root shared by Latin sum and est . The forms was and were are from an Indo-European root meaning ‘remain’. The forms be and been are from an Indo-European root shared by Latin fui ‘I was’, fio ‘I become’, and Greek phuein ‘bring forth, cause to grow’. The origin of are is uncertain.
wiktionary
From Middle English was, from Old English wæs, from Proto-Germanic *was, (compare Scots was, West Frisian was (dated, wie is generally preferred today), Dutch was, Low German was, German war, Swedish var), from Proto-Indo-European *h₂wes-(“to reside”), whence also vestal. The paradigm of “to be” has been since the time of Proto-Germanic a synthesis of three originally distinct verb stems. The infinitive form be is from Proto-Indo-European *bʰuH-(“to become”). The forms is and are are both derived from Proto-Indo-European *h₁es-(“to be”). Lastly, the past forms starting with w- such as was and were are from Proto-Indo-European *h₂wes-(“to reside”).
etymonline
was (v.)
Old English wesan, wæs, wæron 1st and 3rd person singular of wesan "to remain," from Proto-Germanic *wesanan (source also of Old Saxon wesan, Old Norse vesa, Old Frisian wesa, Middle Dutch wesen, Dutch wezen, Old High German wesen "being, existence," Gothic wisan "to be"), from PIE root *wes- (3) "remain, abide, live, dwell" (cognates Sanskrit vasati "he dwells, stays;" compare vestal). Wesan was a distinct verb in Old English, but it came to supply the past tense of am. This probably began to develop in Proto-Germanic, because it is also the case in Gothic and Old Norse. See be.
