To Decide
To Determine
する verb
A 決定 is a "decision." So, when you add する to it you're making it a verb, meaning this word means to decide.
けっていする
The reading is the same as 決定 with する added. Make sure you know 決定 and you'll know this word as well.
コウイチの赤ちゃんの名前が決定したら、すぐにお知らせしますね。
Once they've decided on a name for Koichi's baby I'll let you know right away.
コウイチは、じゅう業いんのきゅうりょうを決定するけん利を持っている。
Koichi has the right to decide his employee's salaries.
クソワロタwwwこのテレビ番組クソほど面白いじゃねーかよ。俺の一番好きな番組に決定したわ。
ROFL! This TV show is hilarious, man. I’ve decided that this is now my new favorite show.