ETYM Icel. skil a distinction, discernment; akin to skilja to separate, divide, distinguish, Swed. skilja. skille to separate, skiel reason, right, justice, Swed. skäl reason, Lith. skelli to cleave. Related to Shell, Shoal, a multitude.
1. Ability to produce solutions in some problem domain; SYN. science.
2. An ability that has been acquired by training; SYN. accomplishment, acquirement, acquisition, attainment.

To make a difference; matter, avail