godan verb (-bu)
live on love; endure for love
Archaic/literary verb meaning to endure hardship or live solely for the sake of love. Not used in modern everyday speech; appears in classical poetry or historical contexts.
古い和歌には「恋い忍ぶ」という表現がよく見られる。
The expression 'koishinobu' is often seen in old waka poems.
Compound of 恋い (koi, 'love', classical form of 恋) + 忍ぶ (shinobu, 'to endure, conceal'). The exact historical derivation is uncertain, but it follows a classical pattern of verb compounding.