Wordnet 3.0
ADJECTIVE (1)
1. 
 not clear and resonant; 
 sounding as if striking with or against something relatively soft; 
- Example: "the dull thud"- Example: "thudding bullets"[syn: dull, thudding]
WordNet (r) 3.0 (2006):
thudding
    adj 1: not clear and resonant; sounding as if striking with or
           against something relatively soft; "the dull thud";
           "thudding bullets" [syn: dull, thudding]