This is the 8057th most frequent Japanese word.
守ろ
"守ろ" is the stem form of "守る," meaning "to protect" or "to guard."
The verb 守る here means to uphold or keep a promise, expressing commitment.
約束を守ります。
I will keep my promise.
The word 守ろう is in its volitional form, suggesting the intention or willingness to protect.
自分の家族を守ろう。
Let's protect our family.
Here, 守る is used in the sense of ensuring the safety or integrity of something—defending a boundary.