expression
Used in superlative expressions with words like 一番, 最も, 最悪 to mean 'the most ... so far' or 'the ...-est to date'. Often appears in the pattern これまでで一番〜.
See also: 今までで (いままでで)
これまでで一番おいしいラーメンだった。
It was the most delicious ramen I've had so far.
これまでで最も難しい試験だった。
It was the hardest exam to date.
Synonymous; 今までで is slightly more common in spoken Japanese, while これまでで can sound a bit more formal or emphatic.
Compound of これ (this) + まで (until) + で (particle indicating scope). The phrase literally means 'within the range up to now'.