sub-aqua
adjective /ˌsʌb ˈækwə/
  /ˌsʌb ˈɑːkwə/
[only before noun] (British English)- connected with sports that are done underwater- sub-aqua diving
- sub-aqua equipment
 Oxford Collocations DictionarySub-aqua is used with these nouns:- diving
 Word Origin1950s: from sub- ‘under’ + Latin aqua ‘water’.