someone who works underwater
"The professional diver carefully inspected the sunken ship's hull before surfacing to report their findings."
Someone who dives, especially as a sport.
"The competitive diver executed a perfect ten-point dive to win the gold medal."
In plain English: A diver is someone who swims down into deep water to look at things underwater.
"The diver held their breath before jumping into the cold water below."
Usage: Use "diver" to refer specifically to someone participating in the sport of diving or underwater exploration; avoid using it casually for anyone simply jumping into water unless they are trained athletes. Do not confuse this noun with the verb "to dive," which describes the action itself rather than the person performing it.
The word diver is formed by adding the suffix "-er" to the verb dive. It originally referred to a person who dives, maintaining that same meaning as it entered common usage.