WordNet sense 1 (a material having capacity or tendency to absorb another substance):

absorbent material

WordNet sense 2 (able to take in large quantities of moisture):

thirsty

WordNet sense 3 (like a sponge in being able to absorb liquids and yield it back when compressed):

spongy

WordNet sense 4 (inducing or promoting absorption):

sorbefacient

WordNet sense 5 (having power or capacity or tendency to absorb or soak up something (liquids or energy etc.)):

absorptive