忍び

Etymology
The of the verb.

Noun

 * 1) the act of putting up with, enduring, bearing
 * 2) a secret or private visit or meeting
 * 3) sneaking; hiding
 * 4) stealth
 * 5) a hidden knife or sword
 * 6) a burglary
 * 1) a hidden knife or sword
 * 2) a burglary

Usage notes
The spelling 忍び with the okurigana may be more common for this reading.