n 1  :  something essential to the appearance or occurrence of something else : esp  :  an environmental requirement <available oxygen is an essential for animal life>   2 a  :  a usu. defective state of health <a serious heart >   b  :  a state of physical fitness <exercising to get into > 
vt, con*di*tioned  con*di*tion*ing   :  to cause to undergo a change so that an act or response previously associated with one stimulus becomes associated with another con*di*tion*able adj 
 
 
 
Similar sounding terms:  con·tu·sion 
 
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