Wordnet 3.0
VERB (2)
1. 
 become covered with clouds; 
- Example: "The sky clouded over"[syn: overcloud, cloud over, cloud up]
2.  become overcast; 
- Example: "the sky clouded over"
WordNet (r) 3.0 (2006):
cloud over
    v 1: become covered with clouds; "The sky clouded over" [syn:
         overcloud, cloud over, cloud up]
    2: become overcast; "the sky clouded over"