This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
孞 is a rare character composed of 子 (child) above 心 (heart). Its historical origin and meaning are uncertain.
A child 子 resting over a heart 心 suggests a tender or sincere feeling, but the exact meaning is unclear.
For シン, imagine a sincere (シン) child's heart: the child 子 above the heart 心 represents pure sincerity, and シン sounds like the beginning of 'sincere'.