Latin law primarily explains Middle East language unit (6)

I believe the answer is:

lexeme

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'language unit' is the definition.
Both the answer and definition are singular nouns.
Maybe there's a link between them I don't understand?

'latin law primarily explains middle east' is the wordplay.
'latin law' becomes 'lex' (I've seen this before).
'primarily' says to take the initial letters.
'middle east' becomes 'me'.
The first letter of 'explains' is 'e'.
'lex'+'e'+'me'='LEXEME'

Can you help me to learn more?

(Another definition for lexeme that I've seen is " Basic language".)

I've seen this clue in The Guardian.

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