What does alkali mean?
An alkali is a chemical substance — strictly, a soluble base — that dissolves in water to form a solution with a pH above 7. Alkalis neutralize acids, feel slippery to the touch in concentrated form, and turn red litmus paper blue. Familiar examples include sodium hydroxide (caustic soda) and potassium hydroxide (potash), substances long used in soapmaking, cleaning, and industry. The word also appears in geology and agriculture: in parts of the American West, an 'alkali flat' is land crusted with mineral salts left by evaporating water, soil too alkaline for most crops. In chemistry, 'alkali metals' names the highly reactive family that includes lithium, sodium, and potassium. The term entered English in the early modern period from Arabic via medieval Latin, its opening 'al-' preserving the Arabic definite article. Related forms include the adjective 'alkaline' and the noun 'alkalinity'.
A compound that dissolves in water to give a solution with pH greater than 7; a soluble base capable of neutralizing acids.
"Sodium hydroxide is one of the most widely used industrial alkalis."
In strict chemical usage, an alkali is a base that is soluble in water; not all bases qualify.
(US regional) Land or soil containing enough soluble mineral salts to be strongly alkaline.
"Cattle grazed warily near the alkali at the edge of the basin."
Common in the American West; often compounded as 'alkali flat' or 'alkali sink'.
Both plurals are accepted; 'alkalis' is more common in British English and modern scientific writing.
"Strong alkalis should be handled only with gloves and eye protection."
The word 'alkali' carries a piece of Arabic in every syllable — it literally begins with 'al', the Arabic word for 'the'.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of alkali
'Alkali' derives from the Arabic 'al-qalī', meaning 'the calcined ashes' — specifically the ashes of saltwort plants used in glassmaking and soap-making. It passed into medieval Latin as 'alkali' and reached English around the late 14th to early 15th century. The initial 'al-' is simply the Arabic definite article, the same element found in borrowed words like 'alcohol', 'algebra', and 'almanac', which share this borrowing pattern rather than a common root meaning.
Related word forms
How alkali is actually used
Chiefly used in chemistry, agriculture, and industrial contexts; register is technical-to-neutral. In everyday speech, 'base' is more common outside scientific settings. Plural is 'alkalis' or less commonly 'alkalies'.
Easily confused with alkali
'Alkali' is a noun naming a specific soluble base, while 'alkaline' is an adjective describing any substance with basic properties.