Ad nutum is an adverbial locution that comes from Latin, and that literally means "with a sign of head." In law it means a decision made immediately, based on an absolute and discretionary power (which does not require any previous conditions, and does not require any justification or explanation).
In France In this country, the expression is used, for example, to typify the freedom of appointment or substitution of high ranking leaders, in which case the mandate implies a very strong trust relationship between the principal and the agent:
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