This is the 14126th most frequent Spanish word.
timbre
A "timbre" in Spanish refers to a doorbell, a stamp (postage), or the tone/quality of a sound.
In this sentence, 'timbre' is used to mean 'doorbell', as it refers to a device used to signal someone inside a building.
Pulsa el timbre para entrar.
Ring the doorbell to enter.
Here, 'timbre' refers to 'tone' or 'quality', specifically related to the distinct character of a sound.
El timbre de su voz era único.
The tone of his/her voice was unique.
Again, 'timbre' denotes 'doorbell', describing the physical device itself.