Wordnet 3.0
ADJECTIVE (1)
1. 
 not slowed or prevented; 
- Example: "a time of unimpeded growth"- Example: "an unimpeded sweep of meadows and hills afforded a peaceful setting"
The Collaborative International Dictionary of English v.0.48:
Unimpeded \Unimpeded\
   See impeded.
WordNet (r) 3.0 (2006):
unimpeded
    adj 1: not slowed or prevented; "a time of unimpeded growth";
           "an unimpeded sweep of meadows and hills afforded a
           peaceful setting"
Moby Thesaurus II by Grady Ward, 1.0:
20 Moby Thesaurus words for "unimpeded":
   clear, disembarrassed, free, open, unblocked, unburdened,
   unchecked, unclogged, unconstrained, unembarrassed, unencumbered,
   unhampered, unhandicapped, unhindered, unladen, unobstructed,
   unprevented, unrestrained, unrestricted, untrammeled