Similar words
mil
millar is more formal, used for counting large quantities, like "millares de personas," thousands of people; mil is the everyday number word.
Similar in other languages
French
mille
mille is the French word for the same thing — both mean "thousand."
Practice
1 What does millar mean?
thousand
2 Fill the gap: Acudieron ___ de personas.
Full sentence: Acudieron millares de personas. (Thousands of people came.)
3 Which fingerprint chart matches millar?
millar: neutral register, common frequency, general domain, neutral connotation.