Plasmid is a biological word, so I guess most people don’t know about the word, but I also heard ( I can be wrong ) native English speakers can presume a word’s meaning by the roots.
As the roots of Plasmid are “plasma” and “id”, where “plasma” can be blood plasma or physical-state plasma (as StoneyB and Andrew point out), while “id” means “shape, form, picture”.
So to a native English speaker who see the word for first time, shall he take it “plasma form”, “plasma shape” or something else? And does it sound like a cool word to you?
Plasmid does not have a long pedigree:
First Known Use: 1952
I used this readability tool, and it rated plasmid as follows:
Your text has an average grade level of about 10. It should be easily understood by 15 to 16 year olds.
Despite this assertion, I did not recognize this word from its biological usage. I may of heard the word in a genetics class that I took in the 1980s and promptly forgotten it.
What about the root word, plasma? Plasma is an ambivalent word, with two biological meanings and two physics meanings (and quartz thrown in for good measure).
1 a green faintly translucent quartz
2 [New Latin, from Late Latin]
a : the fluid part of blood, lymph, or milk as distinguished from suspended material; especially : blood plasma
b : the juice that can be expressed from muscle
4 a collection of charged particles (as in the atmospheres of stars or in a metal) containing about equal numbers of positive ions and electrons and exhibiting some properties of a gas but differing from a gas in being a good conductor of electricity and in being affected by a magnetic field
5 a display (as a television screen) consisting of discrete cells of plasma sandwiched between two layers of glass and electrodes such that each cell emits light when it receives an electric current
(In contrast, the readability tool rated plasma with an average grade level of 7.)
In many schools, they still teach that there are three fundamental states of matter (solid, liquid, gas). But plasma is the fourth state.
Plasma, from Greek πλάσμα, meaning “anything formed”, is one of the four fundamental states of matter, the others being solid, liquid, and gas. (citation)
It sounds like you are tending towards the physics meaning. Yes, the word plasmid sounds cool. Rather than plasmid, I think the alien should take plasma form or plasma-morph and sandwich himself between two sheets of glass and achieve phosphorescence through continuous bombardment of electrons. You could call him TV man.