such a/an
fixed phr.. A2 Elementary Oxford
fixed phr.. you use this to emphasize a quality or to show that something is very impressive or extreme.
fixed phr.. used for emphasis or to indicate degree.
It is such a beautiful day today.
He is such an amazing cook that everyone wants to come to his dinner parties.
The discovery of the ancient ruins was such an unexpected breakthrough that it completely changed our understanding of the region's history.
Usage
Pre-determiner construction that precedes an attributive adjective and a singular countable noun.
Teaching tip
contrast with 'so' (used with adjectives alone) to help students avoid the common 'so a/an' error; 'such' requires a noun to follow.
Pitfall
It was a such nice movie.It was such a nice movie.the word 'such' must come before the article 'a' or 'an'.