freewheel

Short definition from Wiktionary

Noun

1. 1
   A device in a transmission that disengages the driveshaft from the driven shaft when the driven shaft rotates faster than the driveshaft.
2. 2
   The mode or state of operation thus produced: Synonym of neutral.

Verb

1. 1
   To continue spinning after disengagement.
2. 2
   To ride a bicycle without pedalling, e.g. downhill.
3. 3
   To operate a motor vehicle which is coasting without power, e.g. downhill.
4. 4
   To operate free from constraints.