Learner's definition of SUBSTANCE
1 a : a material of a particular kind
b : a drug that is considered harmful and whose use is controlled by law or made illegal
The pancreas secretes a substance called insulin.
The floor was covered with a white, powdery substance that turned out to be flour.
heroin and other illegal substances
He had a history of substance abuse.
Codeine is a controlled substance. [=a drug that you need permission from a doctor to use]
2 a : the quality of being meaningful, useful, or important b : the quality of being true or believable 3 [noncount] : the most basic or necessary part or quality of something : essence
the substance of my argument
These two books differ in both style and substance. [=content]
He stated, in substance [=in essence, essentially], that it is not his fault and he will not pay for damages.
a man/woman/person of substanceliterary
: a person who is rich and powerful