This is the 1078th most frequent German word.
doppelt
"Doppelt" means "double" in English.
Here, 'doppelt' is used to indicate a quantity that is twice as large as another specified amount.
Ich habe doppelt so viel Obst gekauft wie letztes Mal.
I bought twice as much fruit as last time.
In this sentence, 'doppelt' describes the intensification or redundancy of an action (securing).
Diese Tür ist doppelt gesichert, damit sie besonders sicher ist.
This door is doubly secured to ensure it is especially safe.
Here, 'doppelt' conveys a repeated impression, in this case, a visual doubling.