noun
pillory; burden; shackle around one's neck
Literally a wooden frame locked around the neck as punishment; figuratively, a heavy burden or obligation that restricts one's freedom.
借金が首枷になって、自由に動けない。
Debt has become a burden around my neck, and I can't move freely.
昔の罪人が首枷をはめられてさらし者にされた。
Criminals in the past were put in a pillory and exposed to public shame.
足枷 refers to a shackle for the feet or a hindrance, while 首枷 specifically refers to a neck restraint or a burden that weighs on one's mind or freedom.
Compound of 首 (kubi, 'neck') and 枷 (kase, 'shackles'). The figurative sense of 'burden' developed from the literal restraining device.