sonreír
smile
son-
sound
+
reír
to laugh
Sonreír means to smile and can be thought of as a combination of son-0 (sound0) and reír1 (to laugh1), like a soft or soundless laugh.
verb
  1. smile
    To form a smile on one's face.
    Ella no pudo evitar sonreír cuando vio a su hijo. // She couldn't help but smile when she saw her son.