Bad is the opposite of Just. Just is a synonym of Accurate. Accurate is a synonym of Sharp. Sharp is related to Bear. 
Explain is related to Purpose. Device can be used for Purpose. 
Bad <--Antonym--> Just <--Synonym--> Accurate <--Synonym--> Sharp <--RelatedTo--> Bear 
Explain <--RelatedTo--> Purpose <--UsedFor-- Device 