IPA: /ˌsʌbˈeɪkwiəs/
KK: /sʌbˈeɪkwiəs/
Relating to or occurring under water.
The subaqueous plants thrive in the lake's depths.
Subaqueous → It is formed from "sub-" (meaning under) and "aqua" (from Latin, meaning water). The word describes something that is situated or occurring under water.
Think of being 'under' ('sub-') the 'water' ('aqua') — that's why subaqueous refers to something beneath the water.