Wordnet 3.0
ADVERB (2)
1. 
 straight up or down without a break; 
[syn: sheer, perpendicularly]
2.  in a perpendicular manner; 
- Example: "this red line runs perpendicularly to the green line"
The Collaborative International Dictionary of English v.0.48:
Perpendicularly \Per`pen*dic"u*lar*ly\, adv.
   In a perpendicular manner; vertically.
   [1913 Webster]
WordNet (r) 3.0 (2006):
perpendicularly
    adv 1: straight up or down without a break [syn: sheer,
           perpendicularly]
    2: in a perpendicular manner; "this red line runs
       perpendicularly to the green line"