Unilateral meansof, having, affecting, or occurring on only one side.
This is not a commonly used term,. Example in biology Normally unilateral refers to stimulus eg: unilateral stimulus of chemicals or light or touch in tropism. A stimulus is said to be directional or unilateral if it comes from one direction.
Eventhough depending on the context the exact meaning may varry , but Unilateral growth would mean one-sided growth or even growth in one direction.