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Webster 1913 Edition

Adj.

[Pref.

un-

turned

Not turned; not revolved or reversed.

To leave no stone unturned

to leave nothing untried for accomplishing one’s purpose.

[He]

left unturned no stone

To make my guilt appear, and hide his own.

Dryden.

Adj.

Not turned. He left no stone unturned.

unturned ‎(not generally comparable, comparative more unturned, superlative most unturned)

Not turned.
- 1873, Julian Hawthorne, Bressant, ch. 5:
  [W]oman's loveliness had heretofore been an unturned page in the young man's life.