Suffixes creating nouns:
* -ation: observation (the act of observing)
* -er: observer (a person who observes)
* -or: observator (less common, but still used in some contexts)
Suffixes creating adjectives:
* -able: observable (capable of being observed)
* -ant: observant (attentive and noticing things)
Other related words:
* -atory: observatory (a place for observing)
* -ance: observance (the act of observing or following a rule)
Note: Some of these words are less common, but they are still valid formations.
It's important to consider the context and meaning when using these suffixes to ensure the word you create is accurate and appropriate.