clenched fist; iron fist
Refers to a tightly clenched fist, often with a nuance of strength or readiness to strike. Can be used literally or figuratively for harsh enforcement.
He clenched his fist in anger.
The boss struck his subordinate with a clenched fist.
That teacher was known for his iron-fist discipline.
The dictator ruled his people with an iron fist.
After the argument, punches started flying.
punishment by striking with fists; fist punishment
Compound of 鉄 (iron) and 拳 (fist). The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning of a hard, unyielding fist.