The Tocharian B word ṣe-keś
Word ṣe-keś
ʂ e k e ɕ
IPA ʂekeɕ
Meaning once only

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

Other words that might be of interest
ente ‘when’, pikul ‘year’, ompostäṃ ‘afterwards’, postäṃ ‘after’, ṣek ‘always’, śāśvat ‘everlasting’, manta ‘never’