ichidan verb, transitive verb
Used for hiding something on one's person or in a place, often with a nuance of stealth or secrecy. Common in phrases like 懐に忍ばせる (to carry concealed in one's bosom).
彼はポケットに小銃を忍ばせていた。
He had a small pistol concealed in his pocket.
彼女はハンカチに香
She keeps a handkerchief with a hint of perfume hidden on her.