Syn is the pantheon's smallest power and perhaps its most modern one. Every other goddess in Snorri's catalogue presides over something the world desires — love, healing, wisdom, safe passage, the keeping of oaths. Syn presides over the thing everyone needs and no one thanks: the refusal. The door that does not open. The claim that does not stand. Hers is the only divine function in the corpus that is purely negative, and the tradition ranks her, deliberately, 'of no lesser worth' — a household is not safe because its doors are beautiful but because someone holds them shut.
And there is a deeper point folded into the etymology. The word she bears is a law term, kin to the word for truth: the denial is not stubbornness but testimony, the truthful no that answers the false claim. In a mythology that ends with the doors of the world broken down at Ragnarǫk, Syn stands at the threshold for as long as the hall stands — the goddess of the boundary, reminding us that a wall is only architecture until someone is willing to say no.