Description:

The term 'rat' comes from English and other languages and refers to the animal.

It has another sense borrowed from the English sense of 'tattle-tale', but with a broader sense more like 'betrayer', although the sense of betrayal by revealing incriminating privileged information is still there. 

In a verbal context it has the second sense of 'to betray', as a transitive skurun verb without the additional phrasology of something like English 'rat out', taking an ergative betrayer and an absolutive party betrayed.

The modifier form 'ratys' can just mean 'rat-like' in a scientific context, or someone prone to betrayal to save our benefit themselves colloquially.