자발적인 (+noun) · 자발적으로 · 자발적이에요
voluntary, of one's own accord
Example
학생들이 수업 후에 자발적으로 교실을 청소했어요.
The students cleaned the classroom on their own initiative after class.
Word parts
자 self+발 start, emit+적 -ic, -al
Literally 'starting from oneself'.
Good to know
Pronounced [자발쩍]: ㅈ after ㄹ is tensed in -적 words.