doubler

noun

1. One who doubles.
2. An instrument for augmenting a very small quantity of electricity, so as to render it manifest by sparks or the electroscope.
3. A metal plate riveted or welded over a preexisting metal structural component to reinforce it and relieve the stress on the preexisting component, or to serve as a patch where part of the original structure has failed or been removed.

   “The mechanics fastened a doubler over the hole where the cracked section of the plane's skin had been cut out.”

   “The airworthiness directive called for riveting a reinforcing doubler to the wing midspar web to keep the spar from buckling under flight loads.”

4. Part of a distilling apparatus for intercepting the heavier fractions and returning them to be redistilled.
5. A blanket or felt placed between the fabric and the printing table or cylinder.
6. A person employed in a roller mill to fold the hot metal plates in half.
7. A device with two electrical plugs that plugs into an electrical outlet, effectively converting the electrical outlet into two; socket converter.
8. A diaper insert.
9. (US, dialectal)A tenement house having two families on each floor.
10. (colloquial)A biplane aeroplane or kite.