adjective
firm, solid, fixed
B1
fest means firm, solid, or fixed. Adjective used for physical solidity or fixed arrangements. Gradable: comparative fester, superlative am festesten. Common antonyms: locker, flüssig. Can act adverbially (sit tight, hold fast). Not a participle. No irregular forms; regular comparative and superlative.
Examples
Der Boden hier ist fest und stabil.
The ground here is solid and stable.
Der Stuhl ist sehr fest.
The chair is very firm.
Der Termin steht fest, er kann nicht mehr geändert werden.
The appointment is fixed; it can't be changed anymore.
Details
Mnemonics
Imagine a knot tied so tightly that it will not come undone.
Sounds a bit like English 'fast' — think of something held fast/tight.
For adjectives, remember they don't have gender by themselves; attach them to nouns like 'der feste Stuhl'.
Notes
Used both for physical solidity (festes Material) and for fixed/decided situations (ein fester Termin). It is gradable (fester, am festesten).