천륜이 · 천륜을
natural bond of kinship, blood ties
Example
부모와 자식 사이의 천륜은 끊을 수 없어요.
The natural bond between parents and children cannot be broken.
Word parts
천 heaven+륜 moral order
Literally 'heaven's order': family ties no one chooses.
Good to know
Pronounced [철륜]: ㄴ before ㄹ becomes ㄹ.