Command, order, injunction, bidding, behest, mandate, dictate mean a direction, that must or should be obeyed, to do or not do something.
Command imputes to the person who issues the directions either unquestioned authority or complete control of a situation. The term usually connotes either peremptoriness or imperativeness.
Order is not always clearly distinguishable from command; it is, however, the preferred word for directions to subordinates that are instructions as well as commands; in such use it commonly implies explicitness in detail.
Injunction carries a weaker implication of imperativeness than the preceding words except in legal use, where it is applied to a court order commanding a person to do or more often to refrain from doing something on the penalty of being adjudged guilty of contempt of court.
In general use the word stresses admonition without losing the implication of expected or demanded obedience.
Bidding, chiefly literary, usually implies the status of master or parent in the person who issues the orders and therefore stresses expected obedience or the fact of being obeyed.
Behest is also distinctly literary and equivalent to bidding in its implications.
Mandate (see also MANDATE 2) carries the strongest implication of imperativeness of all of these words, for it denotes a command or order issued by a very high, often the highest, authority. It has or has had specific applications, such as an order from a superior court or official to an inferior one or from a Roman emperor to the commander of his military forces.
It is often applied to something inexorably demanded (as by the exigencies of the situation) rather than actually or verbally commanded.
Dictate basically denotes a command given orally. More often it applies to a command or authoritative judgment uttered by an inner voice (as of the conscience) or formulated in a principle or law.