Ten in mesh, subsequently (4)
I believe the answer is:
next
'subsequently' is the definition.
(I've seen this in another clue)
'ten in mesh' is the wordplay.
'ten' becomes 'X' (Roman numeral).
'in' means one lot of letters goes inside another.
'mesh' becomes 'net' (synonyms).
'x' put within 'net' is 'NEXT'.
(Other definitions for next that I've seen before include "Closest" , "Succeeding" , "Coming nearest in order - come, please!" , "Coming nearest in time or sequence" , "Immediately following in time or order" .)