Natyashastra
अङ्गुल्यो यस्य हस्तस्य तलमध्येग्रसंस्थिताः । तासामुपरि चाङ्गुष्ठः सः मुष्टिरिति संज्ञितः ॥ ५५॥
The hand in which the fingers are bent into the palm and the thumb is placed over them is known as Muṣṭi (fist).
english translation
aGgulyo yasya hastasya talamadhyegrasaMsthitAH । tAsAmupari cAGguSThaH saH muSTiriti saMjJitaH ॥ 55॥
hk transliteration by Sanscript