Populace - populous

The two words populace and populous, which sound identical in the mouths of most native English speakers, are different, though closely related, in meaning. (They are virtually homophones; both stress the first syllable, which has the vowel of 'got', IPA: /ɒ/) The difference is largely due to their different word classes.

• Populace is a noun. It is a looser, more general, and altogether more impressionistic word than 'population' - but it means much the same. Unless you have good reason to use populace, prefer population in academic writing.

• Populous is an adjective. It means 'with many people'. "London is a populous city". This is a word you'd be best advised to avoid, in most formal writing. Use, as a substitute, the less stuffy, simpler words such as 'crowded' or 'busy', unless you mean to use 'populous' specifically as a quasi-technical term in subjects like Geography.

(For a related etymological point, you may like to see popular.)