Definitions:

Layperson: someone who is not trained in a particular subject or type of work, especially when they are being compared with someone who is [≠ expert]

Shibboleth: an old idea, custom, or principle that you think is no longer important or suitable for modern times

2007. Dictionary of Contemporary English. 10^th edition. Longman, 1^st edition 1978.

Synchronic: Relating to a language as it is at a particular point in time

Diachronic: Relating to the way a language has developed over time

2005. Oxford Advanced Learner’s Dictionary. 7^th edition. Oxford: Oxford University Press, 1^st edition 1948.