IPA: /ˈsʌbˌsi/
KK: /sʌbˈsi/
Relating to or located beneath the surface of the sea.
The subsea pipeline transports oil from the ocean floor to the shore.
Subsea → It is formed from "sub-" (meaning under) and "sea" (from Old English "sǣ", meaning large body of water). The word "subsea" refers to anything that is located or occurring under the sea.
Think of something that is 'under' ('sub-') the 'sea' — that's what subsea means.
No commonly confused words.