to command: to lay a binding order on someone who is expected to obey it.
At its core this is the word for an order given by someone who has the standing to be obeyed: a king to his servants, a father to his sons, a master to his household, and above all God to people, to nations, even to the sky and sea. It is not just saying words; it is laying a binding instruction on someone, with the expectation that they will carry it out. The Bible's ordinary words for speaking often stand right beside it to report the actual content of the order, while this verb names the act of giving it.
The senses below are not different words but different settings for one act of commanding. The same verb covers a one-time order to do a particular thing, a standing charge to live or teach a certain way, the formal commissioning of a person into a task, the last instructions a dying man leaves, and God's decree that summons an event or even a part of creation into action. What holds them together is authority backed by the right to be obeyed.
It is by far the most common word in the Law for God's commandments. When Israel is told to do all that the LORD has commanded, this is almost always the verb, and the ordinary word for a commandment is built from it. So the word carries much of the weight of the Bible's idea that God's people live under instructions they did not invent and are not free to revise.
Hebrew uses this one verb where the neighboring languages spread the work over several. Aramaic, for instance, says command with a different word entirely. Israel's writers kept this verb almost to itself for authoritative speech, and that is part of why it gathered so much covenant weight: where it appears, the speaking is not a suggestion or a report but an act that creates a duty by being spoken.