My teacher gave a bunch of words to define, and the word, Second hand pill is one of them. What does second hand pill mean ?

Are you sure it was written down right? Did your teacher give you a printed list? Or were the words read to you, and you wrote them down?

This dictionary website searches through a large number of other dictionaries ... and there is no such word in any of them!
http://www.onelook.com/?w=Second+hand+pill&ls=a

To define the term "second hand pill," we can first break it down into its components. "Second hand" typically refers to something that is not directly from the original source but has been used or passed on by someone else. Meanwhile, a "pill" is a small solid oral dosage form that is intended to be ingested.

Considering these definitions, a "second hand pill" could potentially refer to a situation where a pill or medication is not obtained directly from the original source or prescribed by a healthcare professional. It might involve obtaining or taking medications that have been previously used, shared, or acquired without proper medical guidance or supervision. However, I must note that "second hand pill" is not a standard pharmaceutical term and may not have an established definition.

To gain a clearer understanding and ensure accuracy, it's important to consult credible sources such as medical dictionaries, textbooks, or trusted healthcare professionals. Additionally, if you need further clarification from your teacher, I recommend reaching out to them for specific guidance on how to define "second hand pill" within the context of your assignment.