set in
(of rain, bad weather, infection, etc) begin and seem likely to continue (指雨、 壞天氣、 傳染等)開始并可能繼續下去
I must get those bulbs planted before the cold weather sets in. 我得在天氣轉冷之前把這些球莖秧種上.
Those beams will need to be replaced; it looks as though woodworm has set in. 那些大梁該換了, 看樣子里面生了蛀蟲了.