chestnut in its burr
Refers to the spiky husk containing the chestnut; also used metaphorically for a prickly or unapproachable person.
In autumn, chestnuts in their burrs lie on the road.
He looks prickly like a chestnut burr, but inside he's kind.
Usually written in kana; the kanji form 毬栗 is rare.
Katakana spelling sometimes used for emphasis or in informal contexts.
Kanji spelling is uncommon; learners will almost always encounter the kana form.
Compound of いが (burr, prickly husk) and 栗 (chestnut). The exact origin of いが is uncertain, but it may be related to 毬 (iga, 'burr').