Definitions:
Diachronic
/di
kronnik/
• adjective concerned with the way in which something,
especially language, has developed through time. Often
contrasted with SYNCHRONIC.
— DERIVATIVES diachronically adverb diachrony /diakrni/ noun.
— ORIGIN from Greek khronos
‘time’.
Synchronic
/singkronnik/
• adjective concerned with something (especially a
language) as it exists at one point in time. Often contrasted
with DIACHRONIC.
—
DERIVATIVES synchronically adverb.
Layperson – is one who has
ideas about language, ideas which are sometimes absurd. If there´s
any variability, there shouldn´t be any, according to
a layperson.
Shibboleth - a word, phrase,
custom, etc. only known to a particular group of people, which you can use to
prove to them that you are a real member of that group
http://dictionary.cambridge.org/