pure
The German word 'rein' is used to express purity in terms of being free from contamination or pollution. It can be used in various contexts, such as describing food, substances, or even abstract concepts like ideas or intentions. It's important to note that 'rein' is an adjective and should be used in accordance with German grammar rules.
Purely technically it is possible.
In this sentence, 'rein' is used in the context of something being purely, solely, or just, emphasizing that from a technical viewpoint the situation or action discussed is possible.
He went in without knocking.
In this case, 'rein' is used to mean 'in'. This denotes somebody entering a room or building, specifically without performing a generally customary action beforehand, in this case knocking.
We have to keep the truth pure.
Here, 'rein' is used to mean 'pure'. In this instance it is used metaphorically to describe the necessity of keeping the truth unadulterated and untainted.