expression, godan verb (-gu)
cross the threshold; pass the threshold
Literally stepping over the raised threshold of a Japanese-style room; often used in set phrases about entering a place or beginning a relationship.
彼は敷居をまたぐのをためらった。
He hesitated to cross the threshold.
敷居をまたいで部屋に入る。
Step over the threshold and enter the room.
Standard kanji spelling; 敷居 is the usual way to write 'threshold'.
Alternate kanji for またぐ; 跨ぐ is also common but 敷居をまたぐ is the more frequent spelling.
Compound of 敷居 (threshold) + を (object marker) + またぐ (step over). The phrase is straightforward and literal.