The Tocharian B word käṣṣī
Word käṣṣī
k ə ʂ ʂ ī
IPA kəʂʂ੸
Meaning master
See also Avestan: sāstar- ‘master’

Comments
Douglas Q. Adams, “Etymological Dictionary of Tocharian B”, 1999, Brill

Other words that might be of interest
tāś ‘commander’, perneu ‘glorious’, nay ‘governance’, walo ‘king’, wayauca ‘leader’, saswe ‘lord’, klyomo ‘noble’, mäñcuṣke ‘prince’, mäñcuṣka ‘princess’, lāntsa ‘queen’, kamartīke ‘ruler’, oṅkipṣe ‘shameless’