acida

No suffix, and the false one is a busy suffix. -id- is a real and productive Esperanto affix meaning offspring: kato gives katido a kitten, ĉevalo gives ĉevalido a foal, reĝo gives reĝido a prince. So acida invites the reading ac- plus -id- plus -a. There is no root ac-; acid- is one borrowed unit from Latin, and the only offspring in it are the four English cognates. Watch for the same shape in rapida, solida and stupida - all single roots, all wearing the same false costume.

The taste vocabulary, in a set. Dolĉa sweet, acida sour, amara bitter, sala salty, and pika for the sharp burn of chilli. Acida is the everyday word for the taste of lemons and of milk that has gone off, and acidiĝi is what the milk does. For a person, acida rideto is a sour little smile, and the metaphor works the same way it does in English.

The chemistry is the same word. Acido is an acid, acideco acidity, and senacidigi is to neutralise. That the everyday adjective and the laboratory noun share a root is not an accident of Esperanto but an inheritance: chemists named the class of substances after the taste, because tasting things was how the first ones were identified. Vinagro is vinegar, and it is transparently vino plus akra - sour wine - which is exactly what French vin aigre says too.