It's from the Dutch for "cabbage salad"
Apostrophes... [DOC] [TLE] Bobby Flay Coleslaw Makes a Great Accompaniment for Various ... [PAR] May 26, 2016 ... Well, the term coleslaw stems from the Dutch term 'koolsla' which means 
cabbage salad where 'kool' is Dutch for cabbage while 'sla' is its... [DOC] [TLE] Cabbage for Coleslaw | Broad Street Media - Northeast Times [PAR] Aug 11, 2015 ...