Description:

The term.'rat' is an AXZ coining from the early modern period, although similar forms are arrested earlier. It comes from the word 'radiation', modified in typical AXZ fashion to clip off 'unnecessary' derivational endings. The coining was also likely influenced by similar words ratio and raton for the elements radium and radon, and possibly also the CGS system unit of radiation dose, the rad.

In technical language, it has the core meaning of any emission of photons, and/or photon flux, as well as radiation comprised of massive particles, from nearly massless neutrinos to massive atomic nuclei in cosmic rays. The core, unifying principle in a technical context is generally that the source is some kind of nuclear reaction. This term has made it casual, non-technical speech where it strictly refers to dangerous radiation, and can have a metaphorical sense similar to English but more overly negative in connotation. 

Noun: 

In a noun context, 'rat' refers to any product of nuclear reactions from sunlight to cosmos rays when speaking technically, or harmful radiation when speaking colloquially..

The derived form 'ratka' means 'radiation source' in technical speech and does not have a casual sense. 

The derived form 'ratysyn' only has a meaning colloquially and means something or someone that everyone avoids at all costs.

Verb:

In a verb context, 'rat' is an intransitive pali verb meaning to be radioactive. If you want to add what is being radiated, whether literal or metaphorical, you use the null preposition. E.g.:

A eon se rat na eosyn.

The sun radiates light. 

Modifier: 

The derived form 'ratys' means 'radioactive'. In colloquial speech it can mean that literally our metaphorically be extended to describe anything that nobody wants anything to do with.