水中: in the water / 水柱: column of water

一日中: all day, throughout the day, sunrise to sunset, all around the clock

一輪車, 1輪車: a unicycle

一塁手: a first baseperson; a first baseman; a first basewoman

一部始終: the whole story

一日経: dead memorial service where many gather to transcribe a sutra in one day

一網打尽: roundup, wholesale arrest

one part

With your heart and soul. To do something with all of your possible effort.

roundup, wholesale arrest; "rounding up the herd with one throw"