Sentence:  At this point a cock crew, and the youth jumped up hastily saying : 'Of course I shall ride with the king to the war, and if I do not return, take your violin every evening to the seashore and play on it, so that the very sea-<WSD>kobolds</WSD> who live at the bottom of the ocean may hear it and come to you.' 
Meaning of the word marked with <WSD> tags:  An ambivalent, sometimes vindictive, spirit that is capable of materialising as an object or human, often a child; a sprite.