a. (UN-1 7 b.)

1

  Common in recent use. Hence unrid(e)abi·lity.

2

1881.  Daily News, 5 Jan., 6/5. Over a fine open country, till the land became almost unrideable.

3

1883.  C. Howard, Roads Eng. & Wales (ed. 3), 94. Steep unrideable ascents and descents.

4