Buddhist food, room, religious purification, worship, avoid, alike
齋 centers on ritual purity and abstention: religious purification, worship, and the avoidance of impurities. The Buddhist food sense is a specific application of this purified state, and 'room' likely refers to a purified space for such practices.
齋 is the traditional form of 斎. It combines 齊 (uniform, orderly) with 小 (small), suggesting a small, orderly space for purification. The exact historical development is uncertain, but the character is associated with ritual cleansing and abstention.
The outer 齊 suggests uniformity and order, while the inner 小 hints at a small, focused space. Picture a tiny, orderly room where one purifies oneself through worship and avoids impurities, eating only simple Buddhist food.
For サイ, imagine a sigh of relief after purification: sigh -> サイ, as you enter the purified room.