Many beautiful words come into English from a foreign language because English doesn’t already contain a word to exactly fit a certain situation. We might use “homesickness” or “nostalgia” as synonyms to “hiraeth,” but they don’t perfectly match what this Welsh word encompasses. It means “deep longing for something, especially for one’s home.” In its original usage it applies specifically to a longing for Wales, but we can borrow it into English to apply to a longing for any childhood or homelike situation.