Ach/ɑːx/ Definition 1 of 2Pro Tip 1/3Informal Usage Use 'ach' in casual situations, but avoid in formal writing or speaking. Ach, I just missed the bus! Pro Tip 2/3Express Emotion 'Ach' is a way to show feelings quickly, often used in daily conversations. Ach, that's amazing news! Pro Tip 3/3Cultural Color Understanding 'ach' can give insights into the emotions and expressions of British and Irish people. Ach, this rain is typical for London.