I. ˌən-dər-ˈsē adjective
Date: 1613
1. : being or carried on under the sea or under the surface of the sea
undersea oil deposits
undersea fighting
2. : designed for use under the surface of the sea
an undersea fleet
II. adverb
or un·der·seas -ˈsēz
Date: 1645
: under the sea : beneath the surface of the sea
photographs taken undersea