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"
have
The four-letter word that means "inside of" is "within." It is commonly used to indicate something contained or enclosed by something else.
Urge
The word you're looking for is "spontaneous." It means something that occurs naturally or without external influence.
One answer could be "chair" (hair, air).
A five-letter word that means "maybe" is "might."
An Acrostic
shard
have