LaTeX Formatting - Left Margins for Vocab Words

Question

I recently started working with LaTeX. I'm currently using it to take notes from an old math text. I like the formatting here with the vocab word in the left margin before its definition. I was messing with \marginpar to get a similar effect, but I am having trouble recreating it. Any suggestions?

Here is my not so successful attempt. I am less worried about getting my font formatting to work correctly than the margin structure.

\documentclass[letterpaper,12pt]{report}
\usepackage[T1]{fontenc}
\usepackage[margin=1.5in]{geometry}
\usepackage{charter}

\reversemarginpar

\begin{document}

\marginpar{\textbf{Proposition}}\textbf{Definition.} A \emph{proposition}
is an ordinary statement
which one and only one of the words ``true'' or ``false'' can be meaningfully
applied.
\\\\
{\marginpar{\textbf{Open Sentence}} \textbf{Definition.} An \emph{open
sentence} is a statement involving one or more variables which becomes true or
false each time that specific values are given to the variables. These
values must be chosen from a set of numbers that is specified in advance.

\end{document}