A high-pH substance is a material with a pH level higher than 7.0, which is considered to be alkaline. The crossword solutions for the term 'high-pH substance' are BASE (4 letters), ALKALI (6 letters), LYE (3 letters), and ALALI (5 letters). BASE is an acronym for bicarbonate of soda, which is a common BASE used in many household products. ALKALI is a type of BASE that is highly soluble in water and has a pH level higher than 7.0. LYE is a type of ALKALI that is commonly used in soap making. ALALI is another type of ALKALI that is used in industrial processes.