Someone on Quora linked to the Wikipedia article on the ‘Canaanite shift’:
In historical linguistics, the Canaanite shift is a sound change that took place in the Canaanite dialects, which belong to the Northwest Semitic branch of the Semitic languages family. This sound change caused Proto-NW-Semitic *ā (long a) to turn into ō (long o) in Proto-Canaanite. It accounts, for example, for the difference between the second vowel of Hebrew שלום (šalom, Tiberian šālōm) and its Arabic cognate سلام (salām). The original word was probably *šalām-, with the ā preserved in Arabic, but transformed into ō in Hebrew.
The article cites several examples, some of which I had known independently as Arabic and Hebrew forms, but I had never inferred that regular sound shift from them! (Quite possibly because I don’t really know Hebrew and Arabic.)