This is the 758th most frequent Catalan word.
mar
Sea.
Here 'mar' is used in its primary meaning as a noun referring to a large body of salt water, 'sea'.
El mar és tranquil avui.
The sea is calm today.
'Mar' specifies the origin of the waves, linking to the sea as the source of the natural phenomenon described.
Les onades del mar fan un so relaxant.
The waves of the sea make a relaxing sound.
In this sentence, 'mariner' is an adjective derived from 'mar', referring to something pertaining to the sea, such as a seaside location.