A ten letter word for something that occurs could be an occurrence or happenings.
You are looking for the word subaqueous.The definition of subaqueous is "something that us formed or adapted for underwater use" and "something that is found or occurs underwater".An example of a subaqueous object is a submarine.
A four letter word meaning the foundation of something is base.
occurance means "how often something happens or occurs"
What is a 4 letter word that means a foundation of something
have
Urge
A five-letter word that means "maybe" is "might."
Improve
shard
Own
have
An Acrostic