The ornamental design for an armchair, as shown and described.
FIG. 1 is a front elevational view of an armchair showing my new design;
FIG. 2 is a left side view thereof;
FIG. 3 is a perspective view thereof;
FIG. 4 is another perspective view thereof; and,
FIG. 5 is a perspective view thereof with two armchairs piling up to illustrate the armchair can be piled up.
The wicker surface weaving and edge braiding shown in FIGS. 1–4 are representative of the weave and braiding throughout the armchair. They are depicted in fragmented portions to avoid crowding of the drawing.
The broken lines shown form no part of the claimed design.