adverb taking the 'to' particle, taru-adjective
copiously; in torrents; gushing
Describes water, tears, or other liquids flowing abundantly and continuously. Often used with verbs like 流れる, 湧く, 出る. Literary or emphatic nuance.
泉から水がこんこんと湧き出ている。
Water is gushing out copiously from the spring.
彼女の目から涙がこんこんと流れ落ちた。
Tears streamed down from her eyes in torrents.
The exact derivation is uncertain. It is a mimetic or sound-symbolic word imitating the sound or appearance of abundant flowing.