To go ahead is to start or continue without waiting. Permission is not needed, or it has just been given.
As an invitation it is generous, and saying go ahead means please do. The noun the go-ahead means the permission itself, so getting the go-ahead for a project is the moment it becomes real. There is a second sense of proceeding despite something, since an event that goes ahead has not been cancelled, and that is the sense every weather forecast is being checked for.
Practised in Phrasal Verbs, A Man Called Ove
First appears in chapter 2 of A Man Called Ove.
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