If you're asking about how to 'pronounce' the English word "sinister", it would be pronounced something like "shini-staah". In romanji, it would be spelled "shinisutaa".
If you're asking "How do you say "sinister" in Japanese?",
the answer would be "fukitsu na", or 不吉な. Also "magamagashii" (まがまがしい).
不吉
to
Nabigeetaa.
washi
osutoraria
tsuki
maikaru
kore
Steevann
meron
yoru
saigo