at work—
1. at one’s place of employment:
- He’s at work now, but he’ll be back at six.
2. engaged in a particular activity:
- The poor woman was still hard at work at an ironing-table.
3. having a particular influence or effect:
- The same disastrous processes are at work in the whole of this area.
in work—
1. having employment:
- He has been out of work for a year. He’ll be glad to be in regular work again.
2. in process of preparation or completion:
- The company has three films in work right now.
3. (of a horse) in training:
- I had two horses in work during November and December.
Note:
a) The expression does not fully correlate in meaning with the phrase in the works— = in work 2:
- A plan of reorganization is reported to be now in the works.
b) The expression does not correlate in meaning with the phrase in labor—experiencing the pains and efforts of childbirth:
- Vane had been in labor for eight hours before her twin daughters were finally born.