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Word ladder or doublet?
Two names for one puzzle, and why the older one stuck in some places and not others.
Two names for one puzzle
A word ladder and a doublet are the same puzzle. The chain has a fixed length, each step changes exactly one letter, and every word in the middle has to be a real word. Nothing changes when the label does. You can meet the puzzle under both names on the same shelf of puzzle books, and the conditions do not shift between them. Doublet is the older label, and it points back to the puzzle's invention. Word ladder is a description of what you build. Both send you to the same task: start at one word, finish at another, and find the rungs in between.
Who called it what
Lewis Carroll invented the puzzle in the 1870s and called it a doublet. His original problem turned APE into MAN. That name has stayed with the puzzle, and it still turns up in places where the history is part of the appeal. Word ladder is the plain description that sits beside it, used where the rule is the point. Neither label marks a different puzzle. They travel through different kinds of writing rather than different rules, and the conditions under both are equal length, one changed letter per step, and real words throughout.
Why the plain name spread
A name that explains the puzzle does more work than one that needs explaining. Word ladder tells you the shape of the thing: words stacked one above another, each a step from the last, so the task is visible before you read a rule. Doublet carries no such hint. It is a word you have to learn in this context, and nothing in it mentions letters, steps or length. The descriptive name is also the easier one to hand to someone who has never heard of Carroll. That is why the plain name does most of the work now, while the older one survives where the origin is the interesting part.
Other names you may meet
Beyond those two, the puzzle tends to travel under a description rather than a third proper name. A page that wants to avoid both labels will often just state the rule: change one letter at a time, keep every word real, start here and finish there. In practice that sentence is the name, because it is the thing a new solver can act on. It also tells you what to check first. If a puzzle is called something else and then asks you to change one letter per step between two words of equal length, you are looking at a word ladder under another title.
What the label does not change
Whatever the page calls it, the solving stays the same. Par is the number of steps in the shortest possible ladder, found by exhaustive search rather than estimated, so the target is a fact rather than a guess. Up to three hints are available on Rung a Day, and a hint reveals one letter of a shortest route. Four-letter word graphs are denser than five-letter ones, so four-letter ladders are usually easier and shorter, which makes them a sensible place to begin. The name is the last thing to worry about.
Questions
Is a doublet the same as a word ladder?
It is. Doublet is the name Lewis Carroll gave the puzzle in the 1870s, and word ladder is the plain description used beside it. The conditions are identical under both labels: equal length, one changed letter per step, and a real word at every rung.
Why do some pages still say doublet?
Because that is the name the puzzle was invented under. Pages that care about the origin, or that reprint old puzzles, tend to keep it. The label signals the history rather than a different set of rules, so a doublet is solved exactly like a word ladder.
Which name should I use?
Either works. Word ladder is the easier one to explain to someone who has never met the puzzle, since the name describes the shape of the chain. Doublet is more precise in writing about Carroll. What matters is that the rule is stated, not which label is attached.
Play today’s ladder → one puzzle a day, about two minutes.