It is included in a General Toolbar, which is default one. The dictionary is just beside Search. The icon is not very intuitive and one would not guess it means dictionary...
I know, it is not easy to design icons. But most of icons on toolbar are not intuitive and are difficult to see.... I hope it will be improved one day... Just a small advice. It would be handy to make icon outline more contrast. (Some older Onyx icons on toolbar have this light outline.) For example if it is dark, than make a white or light gray "line" around. Also, the simpler icon, the better. Dark icon on almost dark background is almost unrecognisible. I have the susspision that the Onyx programers use colour enviroment for development and not B&W.
I know from my own experience that it is not easy design good icon, so I do not critize the programmers. It is just my small wish and suggestion.