Wordnet 3.0
NOUN (1)
1. 
 sudden restriction on an activity; 
The Collaborative International Dictionary of English v.0.48:
clampdown \clampdown\ n.
   sudden restriction on an activity.
   [WordNet 1.5]
WordNet (r) 3.0 (2006):
clampdown
    n 1: sudden restriction on an activity