I think the easiest approach is to use any of a table environment with 2 columns; tabularx
is probably the most convenient as you only need to set one of the columns. Another approach would be a custom list.
The first example with tabularx

The other example with a custom list

The code to the first example
\documentclass{article}
\usepackage{tabularx}
\begin{document}
\renewcommand\arraystretch{1.5}
\noindent%
\begin{tabularx}{\linewidth}{@{} >{\bfseries}l X@{}}
Bête noire
& A pet peeve A thing or person found particularly unwelcome and to be avoided. \\
Billet doux
& A short love letter or note. \\
Bon appétit
& 'Good appetite' - "Enjoy your food". \\
Bon mot
& Clever, witty remark. \\
Bon vivant
& 'Good liver' - a person who enjoys life, especially 'wine, women and song'. \\
Bon voyage
& Have a good trip. Ça ne fait rien (or sans faire rien) It doesn't matter - often deliberately mispronounced in English as 'San fairy Ann'. \\
\end{tabularx}
\end{document}
The code to the second example
\documentclass{article}
\usepackage{enumitem}
\newlist{phrases}{itemize}{1}
\setlist[phrases]{
font=\bfseries,
align=left,
leftmargin=3em,
labelwidth=\linewidth,
itemindent=\dimexpr\linewidth-3em,
labelsep=0pt,
}
\begin{document}
\begin{phrases}
\item[Bête noire] A pet peeve A thing or person found particularly unwelcome and to be avoided.
\item[Billet doux] A short love letter or note.
\item[Bon appétit] 'Good appetite' - "Enjoy your food".
\item[Bon mot] Clever, witty remark.
\item[Bon vivant] 'Good liver' - a person who enjoys life, especially 'wine, women and song'.
\item[Bon voyage] Have a good trip. Ça ne fait rien (or sans faire rien) It doesn't matter - often deliberately mispronounced in English as 'San fairy Ann'.
\end{phrases}
\end{document}