diff --git a/calc-me.flan b/calc-me.flan
index e0e17a0..dfcccd2 100644
--- a/calc-me.flan
+++ b/calc-me.flan
@@ -120,6 +120,6 @@
 (defn main [args [string]] i32
   (if (< (len args) 2)
     (do (print-line "usage: calc-me \"1 + 2 * 3\"") 1)
-    (match (evaluate (bytes (nth args 1)))
+    (match (evaluate (bytes (at args 1)))
       (Some v) (do (print-f64 v) (print-line "") 0)
       None     (do (print-line "calc-me: cannot parse") 1))))
diff --git a/lib/check.ml b/lib/check.ml
index 59ba57f..508c7e7 100644
--- a/lib/check.ml
+++ b/lib/check.ml
@@ -1128,7 +1128,7 @@ and named_call ctx ~want loc name args =
      | other -> fail loc "len takes an array, a slice or a string, found %s"
                   (Types.to_string other));
     prim Tast.Len index_ty [ a ]
-  | "at" | "nth" ->
+  | "at" ->
     (match args with
      | target :: idx when idx <> [] ->
        let target = check ctx target in
diff --git a/plan.org b/plan.org
index e635d9c..0011baf 100644
--- a/plan.org
+++ b/plan.org
@@ -104,7 +104,7 @@ world.
   is type-directed: ~(defvar enemies (Map string Enemy) (map-new))~. ~get~
   returns ~(Option V)~; ~put~ is the `Unit`-returning upsert. See
   spec-memory.md for the deferred move-aware operations.
-- Operations: ~get~, ~put~, ~remove~, ~push~, ~pop~, ~nth~, ~len~, ~update~.
+- Operations: ~get~, ~put~, ~remove~, ~push~, ~pop~, ~at~, ~len~, ~update~.
   Copying is explicit: ~(clone m)~, and owning containers move rather than copy on
   assignment. No ~!~ convention — nothing is immutable, so it
   would carry no information. No ~assoc~; it only existed as the copy-returning form.
diff --git a/sand.flan b/sand.flan
index ce84c07..adbb6d4 100644
--- a/sand.flan
+++ b/sand.flan
@@ -82,7 +82,7 @@
                      (>= c 0) (< c (- cols 1))
                      (empty-at? r c)
                      (< (rand-f32) 0.5))
-            (set (at grid r c)     (nth colors current-color))
+            (set (at grid r c)     (at colors current-color))
             (set (at velocity r c) 1.0)))))))
 
 (defn move-grain [from-row i32  from-col i32
@@ -198,7 +198,7 @@
                            rl/white)
       (rl/draw-texture brush 20 50 rl/white)
       (rl/draw-texture-v brush (rl/Vector2 {:x 44.0 :y 50.0})
-                         (rl/get-color (nth colors current-color)))
+                         (rl/get-color (at colors current-color)))
       (rl/draw-texture-ex brush (rl/Vector2 {:x 72.0 :y 46.0}) 0.0 2.0 rl/white)))
   ;; The mirrored one beside them, scaled up so the flip is visible rather
   ;; than eight pixels wide. If the two badges look the same, either the flip
@@ -449,7 +449,7 @@
 ;; and does not.
 (defn draw-world-cursor []
   (let [p    (rl/get-screen-to-world-2d (rl/get-mouse-position) view)
-        tint (rl/get-color (nth colors current-color))
+        tint (rl/get-color (at colors current-color))
         x    (.x p)
         y    (.y p)
         r    (f32 (* brush-size cell-size))]
@@ -528,7 +528,7 @@
           sh (- (rl/get-screen-height) 40)]
       (dotimes [i (len colors)]
         (let [cx (- sw (* (- (len colors) (+ i 1)) 46))
-              c  (rl/get-color (nth colors i))]
+              c  (rl/get-color (at colors i))]
           (rl/draw-circle cx sh (f32 16.0) c)
           (when (= i current-color)
             (rl/draw-circle-lines cx sh (f32 22.0) rl/white))))
diff --git a/syntax-sketch.flan b/syntax-sketch.flan
index 23f1d03..3afe994 100644
--- a/syntax-sketch.flan
+++ b/syntax-sketch.flan
@@ -58,7 +58,7 @@
 ;; this frame (spec-memory.md, non-escaping fn).
 (defn largest [xs [a]  gt (Fn [a a] bool)] (Option a)
   (if (> (len xs) 0)
-    (Some (reduce (fn [x y] (if (gt x y) x y)) (nth xs 0) xs))
+    (Some (reduce (fn [x y] (if (gt x y) x y)) (at xs 0) xs))
     None))
 
 ;; (largest hps >)   — `>` at i32 is an ordinary function value
diff --git a/test/programs/nth-gone.flan b/test/programs/nth-gone.flan
new file mode 100644
index 0000000..e338553
--- /dev/null
+++ b/test/programs/nth-gone.flan
@@ -0,0 +1,11 @@
+;;;; nth was an alias of at, and an asymmetric one: the checker accepted it as
+;;;; a read, but parse.ml and place_of_expr both match only [at], so
+;;;; (set (nth a i) x) and (addr (nth a i)) were refused while the [at] forms
+;;;; worked. Two names documented as identical that disagree about writing are
+;;;; worse than one name, so nth is gone and this pins the removal: it must
+;;;; fail as an unknown name, not quietly resolve to at again.
+
+(defvar a [4 i32])
+
+(defn main [] i32
+  (nth a 0))
diff --git a/test/test_acceptance.ml b/test/test_acceptance.ml
index 21ac026..398a605 100644
--- a/test/test_acceptance.ml
+++ b/test/test_acceptance.ml
@@ -620,6 +620,11 @@ let () =
       "one directory is one set of names";
     refuses "two mains in one program" "programs/pkg-two-mains.flan"
       "main is defined twice";
+    (* nth is gone, not renamed: it has to fail as a name nobody defined. If it
+       were ever re-added as an alias of [at] it would have to be a place too,
+       and this row is what says so. *)
+    refuses "nth is not a name" "programs/nth-gone.flan"
+      "unknown function nth";
 
     (* ── wasm32 (NEXT.md, deferred item 6) ──────────────────────────────
        The second target, and the reason sand-headless imports no raylib. What
diff --git a/web/index.html b/web/index.html
index 5ec6791..73e630d 100644
--- a/web/index.html
+++ b/web/index.html
@@ -643,8 +643,9 @@ second
 
 <h2 id="arrays">Arrays and slices</h2>
 
-<p><code>at</code> and <code>nth</code> are the same operation and take any number of
+<p><code>at</code> indexes a fixed array or a slice, and takes any number of
 indices, so <code>(at grid r c)</code> indexes a two-dimensional fixed array directly.
+It is a place: <code>(set (at grid r c) v)</code> and <code>(addr (at grid r c))</code> both work.
 <code>len</code> works on a fixed array, a slice or a string.
 <code>(slice s lo hi)</code> takes a half-open range and never copies.</p>