• 志望しぼう — aspiration, wish (e.g. school or job)
• 意志いし — will, determination
• 志願しがん — application, volunteering
• 有志ゆうし — volunteers, willing participants
• 志士しし — patriot, man of high ambition

志 is formed with 心 (heart) and 士 (gentleman/scholar) — expressing the heart’s commitment to a cause. It often refers to ambition, determination, or noble willpower.

彼かれは 医者いしゃになるという志こころざしを持もっている。
He has the ambition to become a doctor.

志望校しぼうこうに 合格ごうかくできました。
I was accepted into my desired school.

The on-yomi シ is used in compounds like 志望 and 意志. The kun-yomi こころざす and こころざし are more poetic or formal, often seen in literary or personal expression.