What does the cryptic crossword clue "Primordial matter found in mouldy lemons (4)" mean?

The wordplay uses a hidden word. Hidden or ‘found’ in mouldY LEMons – we had to check this one The answer is YLEM.

Primordial matter found in mouldy lemons (4)

Independent Cryptic #11751 | 12 Across | 2024-06-08 flower