(a.) Capable of being pressed together\ or forced into a narrower compass, as an elastic or spongy substance.

Spartan Spartanic acerb acerbic acid acidulous acrid acrimonious alum amaroidal ascetic asperous austere authoritarian biting bitter bitter as gall brisk caustic clamp coarse collapsible compactable compressible compressor constrictor constringent consumptive contractible contractile contractional contractive contractor cutting deflationary demanding double-edged dour edged escharotic exacting exigent fierce foldable grim hard harsh incisive inclement irritating keen meticulous mordacious mordant mortified nose-tickling penetrating piercing pincer piquant poignant puckery pungent restorative rigorous roborant rough rugged scathing severe sharp sour stabbing stern stinging strict strident stringent styptic styptic pencil tart tough trenchant ungentle unsparing vehement violent virulent vise vitriolic