candlebomb

from The Century Dictionary.

• noun A small glass bubble filled with water, which when placed in the wick of a candle explodes from the force of the steam that is generated.

from the GNU version of the Collaborative International Dictionary of English.

• noun A small glass bubble, filled with water, which, if placed in the flame of a candle, bursts by expansion of steam.
• noun A pasteboard shell used in signaling. It is filled with a composition which makes a brilliant light when it explodes.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A small glass bubble, filled with water, which, if placed in the flame of a candle, bursts by expansion of steam.
• noun A pasteboard shell used in signaling, filled with a substance which makes a brilliant light when it explodes.