"rumbling" in the noun sense
1. rumble, rumbling, grumble, grumbling
a loud low dull continuous noise
"they heard the rumbling of thunder"
"rumbling" in the verb sense
1. rumble, grumble
make a low noise
"rumbling thunder"
2. grumble, growl, rumble
to utter or emit low dull rumbling sounds
"he grumbled a rude response"
"Stones grumbled down the cliff"
"rumbling" in the adjective sense
1. grumbling, rumbling
continuous full and low-pitched throbbing sound
"the rumbling rolling sound of thunder"
Source: WordNet® (An amazing lexical database of English)
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