observance

What it means

1. countableuncountableThe practice of complying with a law, custom, command or rule.
2. countableuncountableThe custom of celebrating a holiday or similar occasion.
3. countableuncountableObservation or the act of watching.

In a sentence

Thomas Merton was a monk in the Order of Cistertians of the Strict Observance.

Where it comes from

1. Latinobservantia
2. Old Frenchobservance
3. Englishobservance

From Old French observance, from Latin observantia. Equivalent of observe + -ance.