1. To penetrate, absorb, or soak into something. If the water sinks into the floorboards, it could warping or even rot. It takes a few hours for the mixture to sink into the skin.

2. To enter into some passive, non-functional state. Within seconds I had sunk into a deep, dreamless sleep. After staring at the swinging watch, she sank into a hypnotic trance.

3. To force, press, or impale something into someone or something. In this usage, a noun or pronoun is used between "sink" and "into." He sank the blade into the body of his enemy. The farmer sank the stakes of the fence into the ground with several swings of her sledgehammer.

4. To expend time, money, or other resources into someone or something as an investment, especially when those resources were or seem to have been squandered. In this usage, a noun or pronoun can be used between "sink" and "into." By the time the product was finally released onto the market, there was simply no way for the company to earn back what they had sunk into it. We sank a lot of hours into creating this program—if it doesn't work, I'm going to be very disappointed. The company sank so much money into me, between the training courses and masters degrees they paid for, that I feel guilty quitting.