Good Morning
A singular, slightly more concise version of 'Buenos días'. Very common in many Latin American countries like Argentina and Mexico.
A very common, informal abbreviation. It can be used for 'good morning', 'good afternoon', or 'good evening'. The context and time of day make the meaning clear.
Good morning, sir. How are you?
Good morning! Shall we go for a walk?
Upon entering the store: 'Good morning'.
I ran into my neighbor and said: 'Morning, all good?'.
'Buenos días' is the universal standard. 'Buen día' is also extremely common and can be the preferred form in some countries. 'Buenas' is a widespread informal shortcut.
'Buenos días' is the standard greeting. 'Buen día' is understood but used less frequently as a greeting compared to Latin America. 'Buenas' is also common informally.
Both 'Buenos días' and 'Buen día' are used interchangeably and are extremely common. 'Buen día' can sometimes feel slightly more casual or friendly.
'Buen día' is arguably more common than 'Buenos días' in everyday, one-on-one conversations.
'Buenos días' is the most common and polite form. 'Buen día' is also used and understood perfectly. 'Buenas' is very frequent in casual situations.
Saying 'Bueno día' or 'Buena día'. — The word for day, 'día', is a masculine noun, even though it ends in '-a'. The greeting is plural ('Buenos días') or uses the shortened masculine adjective ('Buen día'). 'Bueno día' and 'Buena día' are incorrect.
Using 'Buenos días' in the afternoon or evening. — 'Buenos días' is only used in the morning, generally until noon or the lunchtime meal. After that, you must switch to 'Buenas tardes' (Good afternoon). It does not mean 'Good day' in a general sense.
Thinking 'Buen día' is less correct than 'Buenos días'. — Both are perfectly correct. The usage is regional and stylistic. 'Buenos días' is literally 'Good days' (plural), a traditional way of wishing someone well for many days to come. 'Buen día' ('Good day', singular) is a modern evolution that is standard in many places.