i-adjective
Colloquial, often affectionate or mildly teasing way to describe someone or something as thin or slender. Softer than 細い and carries a casual, familiar tone.
See also: 細い
あの子は手足が細っこいね。
That kid has such skinny arms and legs, huh.
この猫、細っこくて心配になるよ。
This cat is so thin it makes me worry.