Definition from Wiktionary, the free dictionary
כַּאֲשֶׁר • (ka'ashér)
- When, as, at the time that.
- Used other than as an idiom: see כ־, אשר.
- In modern use, this term is comparatively formal, the shorter synonym כְּשֶׁ־ (k'she-) being comparatively informal.
- Unlike English when, כַּאֲשֶׁר is not used in framing questions, nor in introducing interrogative content clauses; the interrogative adverb and conjunction מָתַי (matái, “when”) is used for these purposes.
- Whereas in English, when and that are somewhat interchangeable in introducing complement clauses for temporal nouns — “the time when” and “the time that” being synonymous — in Hebrew כַּאֲשֶׁר cannot be used this way; rather, אֲשֶׁר (ashér, “that, which”) or (more frequently) שֶׁ־ (she-, “that, which”) is required.