A somewhat formal or literary term for giving thoughtful advice or a suggestion, often with a nuance of heartfelt consideration.
I received advice from my senior colleague, which was very helpful.
Thanks to his suggestion, I was able to solve the problem.
Compound of 心 (こころ, heart/mind) and 添え (そえ, adding/attaching), literally 'adding one's heart'. The exact historical derivation is uncertain, but it conveys the idea of offering one's heartfelt thoughts as advice.