Of or pertaining to. Adjectival suffix appended to various words, often nouns, to produce an adjective form. Often added to words of Latin origin, but used with other words also. · Forming nouns, especially of verbal action.
From French costal and its etymon Medieval Latin costālis, from Latin costa (“rib”). As a Spanish unit, via Spanish costal. By surface analysis, costa + -al. Piecewise doublet of coastal.