A substance is a material of a particular kind or a drug that is considered harmful and whose use is controlled by law or made illegal.
You could study for your answers rather than let someone else provide them.
No! You can not define weight in terms of weight. When you define anything in terms of itself, you do not have a definition, you have a tautology. Such is not science but scientism. It is a fraud. One definition could be the attractive force two masses exert when they attract each other.
a set chromosome define about progeny which could be male or female
a person attenting a hospital
identify and define the elements of the communication process
A blog could be defined in a vivid nature if that is how you felt about the blog. If you feel passionate about something you will probably define it in a vivid manner.
Define "you".
Physical phenomena that could be used to define a time could be several things. Some are a balance wheel in a watch, a star, quartz crystals in watches, months, and years.
It is not a standard notation, but it could define either an application whose data update/retrieval model is based on database queries rather than files, or it could mean an application whose main purpose is to query data sources.
Define who "they" are. You could be suspended from the site if you ask generic questions.
15 kilowatts is a measurement of electrical power.
That depends what you define as a "pencil". I could live with pen and stylus.