Sentence:  The B<sub>6</sub>-type octahedral borons are each bonded to five other <WSD>boron</WSD> atoms; four are part of the same octahedron, and one is external to this octahedron. 
Meaning of the word marked with <WSD> tags:  (Q618)The chemical element ("symbol" B) with an atomic number of 5, which is a metalloid found in its pure form as a dark amorphous powder.