The Spanish manuscript may have many leaves (4)
I believe the answer is:
'may have many leaves' is the definition.
(I've seen this before)
'the spanish manuscript' is the wordplay.
'the spanish' becomes 'el' ('the' in Spanish).
'manuscript' becomes 'ms' (abbreviation for manuscript).
(Other definitions for elms that I've seen before include "rugged feature of country churchyard" , "Trees sound like Cockney steering devices" , "may have many leaves" , "Mel's strange trees" , "Trees (of late, prone to disease)" .)