n :  a person or thing that takes the place or function of another <father and mother s>  substitute adj 
, vt, -tut*ed  -tut*ing  :  to put or use in the place of another: as  a  :  to introduce (an atom or group) as a substituent  b  :  to alter (as a compound) by introduction of a substituent .
 
 
 
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