1An onomatopoeic adverb describing something gushing or flowing profusely (e.g. sweat or blood).
暑さで汗がだくだく流れてシャツが張り付いた。
I was so hot that sweat gushed out and my shirt stuck to me.
事故で出血がひどく、シャツがだくだく濡れていた。
The bleeding was severe from the accident; his shirt was soaked with blood.
湯船に湯を注ぐと、だくだくと音を立てて溢れた。
When I poured water into the tub, it gushed and overflowed with a splashing sound.
2An onomatopoeia for a strong, pounding heartbeat (thump-thump; pit-a-pat).
面接で緊張して心臓がだくだくしてしまった。
I got so nervous in the interview that my heart was pounding.
階段を駆け上がったら胸がだくだくした。
After running up the stairs my chest was pounding.
3An onomatopoeic word for the sound of hoofbeats (the rhythm of hooves striking the ground).
夜道に馬の蹄がだくだくと響いてきた。
On the night road the hoofbeats sounded with a dakudaku rhythm.