Non-acidic staple (5)
I believe the answer is:
basic
'staple' is the definition.
(synonyms)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for basic that I've seen before include "Fundamental, elementary" , "No-frills" , "Simple, unadorned" , "Without frills" , "Fundamental; alkaline" .)