The term 'alkali opposite' refers to the opposite of an alkali, which is an ACID. The crossword solutions for this term are ACIDS (5 letters), ACID (4 letters), BASE (4 letters), lithium (7 letters), LITMUS (6 letters) and LYE (3 letters). ACIDS are substances that have a sour taste and can corrode metals, while bases are substances that have a bitter taste and are slippery to the touch. Lithium is a chemical element that is often used in batteries, while LITMUS is a type of dye that changes color when exposed to an ACID or BASE. LYE is a type of caustic alkali that is used in soap-making.