The word "brittle as glass" might refer to something that is delicate and fragile, and may break easily. Some synonyms for this phrase could include "fragile like porcelain," "delicate like lace," or "brittle as ice." Another possible synonym could be "crisp as a cracker," which implies a brittle texture that can easily snap or crack. Other synonyms might include "frail as a leaf," or "reactive like a chemical compound." Essentially, any description that emphasizes fragility, delicacy, or breakability could be used as a synonym for "brittle as glass".