The use of the term synthetic in the case of Tleiaxu spice is most probably correct. In chemistry a synthetic chemical is one derived through chemical reaction(s) of reagents, and not obtained naturally. The process is referred to as a chemical synthesis, and the field is called synthetic chemistry.
Freak is absolutetly spot on when he says that the synthetic spice from the tanks is
melange. A synthetic compound is identical to it's counterpart formed in nature. The term synthetic only indicates it's origin.
Of course nature doesn't just magic up complex molecules and these are often formed in a similar fashion to what we might cook up in the lab through many stages in a synthesis.
I say probably above because you might argue that Tleiaxu spice is formed 'naturally' i.e
. in a living host but it is not produced through the sandtrout life cylce. Also I seem to recall we got a good glimpse of an Axoltl tank at one point and it seemed to me that the raw chemicals were fed into the tank, which acts as some form of chemical reactor.
Confusing terminology perhaps, especially the use of artificial which can imply a difference between the man-made item and nature's handiwork. The term synthetic (in chemistry) was first coined by Kolbe in the mid-1800s. Many others at the time believed that natural complex organic molecules could not be made in such a fashion as they would lack some sort of supernatural component. Personally, in the case of Tleilaxu spice, I think the term engineered might be the most appropriate.
When axolotl tanks arrive in the workplace we may need to rethink our terminology?