Hedor vs. peste vs. olor
In the Spanish language, hedor, peste and olor all carry the connotation of a smell, but each comes with its contextual nuances and subtleties. Their connotations and usage can largely determine which of these words is most appropriate to use in a given situation.
Hedor
B2Hedor refers to an unpleasant, strong or intense smell. However, it does not imply a source or cause like peste.
El hedor de la basura es insufrible.
(The stench from the garbage is unbearable.)
El hedor en la habitación después de una fiesta siempre es desagradable.
(The stench in the room after a party is always unpleasant.)
Peste
B2Peste usually denotes a very unpleasant smell, often related to sickness or decay. It can also literally mean plague and sometimes used as metaphorical for anything severely disliked.
La peste de los cadáveres era abrumadora en el campo de batalla.
(The stench of the dead bodies was overwhelming on the battlefield.)
Había peste a alcantarillado en toda la ciudad.
(There was a sewage stink throughout the city.)
Olor
A2Olor is the most general term among these words meaning any kind of smell, be it pleasant or unpleasant. Unlike hedor and peste, olor can be qualified with modifiers to describe specific type of smells.
Este perfume tiene un olor delicioso.
(This perfume has a delightful smell.)
Hay un olor extraño en esta habitación.
(There is a strange smell in this room.)
Summary
While hedor, peste, and olor all refer to some kind of smell in Spanish, they each convey their own unique additions to that basic concept. Hedor suggests a severely unpleasant scent, while peste adds a sense of lingering illness or decay. On the other hand, olor serves as an all-encompassing term for any kind of smell - good, bad or otherwise.