In
ListLinePlot[{RandomReal[4, 6], RandomReal[2, 8], RandomReal[10, 12]},
AxesLabel -> {"\!\(\*SuperscriptBox[\(N\), \(b\)]\) de sièges",
"Sièges parSyndicat"}, PlotLabels -> {"FO", "SM", "SdM"}]
how can we guarantee that the Axes Label
{"\!\(\*SuperscriptBox[\(N\), \(b\)]\) de sièges", "Sièges parSyndicat"}
is not cut like in this example: