immobile in inglese:

The man lay motionless.

Tom stood motionless, listening carefully.

a motionless scene

she sat motionless for thirty seconds

... a difficulty, yet a motionless, unwearying struggle, congenial to...

These special characteristics explain its preference for still-hunting (lying motionless beside a seal's breathing hole, waiting for one to surface).

The tree stands motionless, clothed in twilight, thickly bedecked with dewdrops.