“Skookum” has a range of positive meanings. The word can have meanings from 'good,' to 'strong,' 'best,' 'powerful,' 'ultimate,' 'brave' and 'first rate’.
Being called “Skookum” may also mean that someone can be counted on as reliable and hard-working, or is big and strong.
A related word “Skookumchuck” means turbulent water or rapids in a stream or river, i.e. "strong water" ("chuck" is Chinook Jargon for "water" or "stream" or "lake").