The leaves of a special herb called Kush were required by gurus as part of daily rituals they performed, but the leaves were very difficult to remove as they were needle like therefore it required expertise and skill to efficiently remove the leaves from the herb. So students were trained with these skills to remove the leaves, once becoming an expert at this task they were sent to remove the leaves from the Kush herb and they were given the name of Kushal. Eventually with the passage of time anyone being an expert in any particular task was called Kushal and hence the name evolved.
According to Maneka Gandhi's book of Sanskrit names, the name Kushal means: Skilled; efficient; right; good; happy; clever; cool; auspicious; proficient; skill; strategy; efficiency. Another name for Shiva.