that which holds firm and can be relied on: faithfulness in a person and truth in a word, as one undivided idea
Hebrew packs into one word what English has to split in two. Emet covers both the truth of a statement (it matches the facts) and the faithfulness of a person (they keep their word and do not let you down). Underneath both is a single picture, taken from the root the word grows out of: something firm, something that bears weight, something you can lean on without it giving way. A sure sign, a tested road, a witness who does not lie, a God who keeps covenant: all of these are emet because all of them hold.
Because it is one idea and not two, the three senses below shade into each other rather than standing apart. The same word names a peg set in a sure place, a king who walks loyally before God, and a report that turns out to be accurate. Which English word fits best, "truth" or "faithfulness," is decided by the sentence around it, not by a different underlying word.
The richest uses are relational. Paired with chesed (חֶסֶד), loyal love, the word fills out the most famous description of God in the Hebrew Bible (Exodus 34:6), where it means that God can be counted on to do what loyal love promises. In those settings the English word "truth" is too thin: the point is not that God states facts accurately but that God is utterly dependable. Yet the same word is also used flatly for plain accuracy, as when the Queen of Sheba says the report she heard was true. Both poles are genuine, and reading the word well means letting each context say which one is in view.