monk; friar
Specifically refers to a Christian monk or friar, not a Buddhist monk (which is usually 僧 or 坊さん).
Ten monks live in that monastery.
修道士 refers to a male Christian monk, the direct gender counterpart to the female 尼僧 in its Catholic sense.
From 修道 (shūdō, 'religious training' or 'monasticism') + 士 (shi, 'person of a certain profession'). The term was coined to refer to Christian monastics.