Definition of "water-cap" [water-cap]

• A form of cylindrical diaphragm of copper in the time-fuse of a shell, intended to prevent the fuse from being extinguished by water in ricochet firing. (noun)
• A bird of the subfamily Fluvicolinæ, the species and genera of which are numerous. Also water-chat. See cut under Fluvicola. (noun)

The Century Dictionary (Public Domain)

• "To do this, unscrew the water-cap and back the paper case out from the lower end with a drift and mallet; cut off from the lower end with a fine saw, or sharp knife struck with a mallet, the proportional part required, and insert the upper part in the stock, forcing it down with a few gentle blows with the drift; screw on the water-cap."
• "All the Navy time-fuzes -- paper case as well as metal stock -- being intended for use under a water-cap, burn a longer time in the open air."
• "A similar effect is produced when the fuze is confined under a water-cap, as in the naval time-fuze."