As a continuation of the topic – Spanish words that are used only in plural form – I now offer you the opposite possibility, namely the so-called Singularia tantum – Only in singular
Only in singular form are, for example
1. Certain words
el cenit – zenith
el caos – chaos
la sed – thirst
2. Collective nouns
la gente – people (although in colloquial language 'las gentes' is increasingly heard)
el dinero – money
3. Substances
la plata – silver
el oro – gold
el cobre – copper
el silicio – silicon, etc.
4. Abstract nouns
la belleza – beauty
5. Names of sciences and arts
la física – physics
la química – chemistry
la historia – history
la medicina – medicine; (in plural form the meaning is different: las medicinas – medicines)
la pintura – painting, etc.