You are frying onions in a frying pan used for meat, when you remember you used a dairy knife to cut the onion, what is the din of the onions? And what is the din of the frying pan? What would be the din in a case that the onions were cut with a meat’e knife; do you have to wait 6 hours before eating milk?
The onions are not kosher, and the pan also needs to be kashered.
One does not have to wait 6 hours for onions cut with a meaty knife.
Shulchan Aruch Y:D 96 1-2
Sefer Davar Charif pg 11 in the name of Rav Elyashiv. cf. Pri Megadim O:C 494:6 Eshel Avraham