No-turn mattress. Rotate regularly.Rotate and turn are one of many pairs of words that English has that are more or less synonymous but come from different sources. Typically, the one that we get from Romance (French or Latin) is used in more formal contexts or has a technical sense: here, that word is rotate. The Germanic counterpart (here, turn) is usually used in a more everyday sense.
That works for this pair. The OED has examples like The whole stage rotates concentrically and the kid turns on the spit, where each could be substituted for the other. The definitions are also more or less identical:
Turn (intrans): to move round on an axis or about a centreWe actually have the transitive senses here, as there is an implied object the mattress, but the transitive definitions are based on the intransitive ones.
Rotate (intrans): to turn about a centre or axis
The above discussion implies that it ought to be contradictory to say no-turn; rotate regularly, as how can you rotate something that can't or needn't be turned? Of course they mean it doesn't need to be flipped over, but you should turn it 180 degrees about its vertical axis (is that what I mean?? the thing stays flat, anyway) now and then to make sure it wears evenly. Here's an example of a pair of synonyms getting put to use in a situation where two different words meaning turn are needed. If one were so inclined, one could check whether the specific meanings each has (turn = flip over and rotate = stays flat) were generally consistent or if it's random which is used for which. That'll have to wait for another day, though, unless one of my readers wants to do it.