in pain—suffering physical pain or discomfort caused by injury or disease:
- They lay rolling themselves on the ground, heavily groaning in pain.
in pains—
1. (of a woman) in the throes of childbirth:
- I remember that in the film, the husband of the woman in pains was sitting far from the scene.
2. = in pain:
- She saw herself test it on a criminal—a rapist, and she saw how much he was in pains.
3. (followed by Infinitive) making a particular effort to do smth.:
- He was in pains to stress that the main task of government was the defense of the rich against the poor.
Note: The expression does not fully correlate in meaning with the phrase at pains— = in pains 3:
- Linda was at pains to see that no one was left out.