noun
Specifically the root of a plant, often with a colloquial or slightly childish feel compared to 根 (ね).
雑草の根っこをしっかり抜いてください。
Please pull out the weed roots thoroughly.
noun
Refers to the remaining stump after a tree has been cut down; the base part still in the ground.
木を切ったあと、根っこが残っている。
After cutting the tree, the stump remains.
noun
Figurative use for the fundamental cause or origin of a problem, similar to 'root' in English.
この問題の根っこは、コミュニケーション不足だ。
The root of this problem is a lack of communication.