The Collaborative International Dictionary of English v.0.48:

Knee-deep \Knee"-deep`\, a.
   1. Rising to the knees; knee-high; as, water or snow
      knee-deep.
      [1913 Webster]

            Grass knee-deep within a month.       --Milton.
      [1913 Webster]

   2. Sunk to the knees; as, men knee-deep in water.
      [1913 Webster]

            Where knee-deep the trees were standing.
                                                  --Longfellow.
      [1913 Webster]

WordNet (r) 3.0 (2006):

knee-deep
    adv 1: up to the knees; "we were standing knee-deep in the
           water" [syn: knee-deep, knee-high]
    adj 1: coming only to the ankle or knee [syn: ankle-deep,
           knee-deep]