Weed let slip after the one here
I believe the answer is:
thistle
'weed' is the definition.
(thistle is a kind of weed)
'let slip after the one here' is the wordplay.
'slip' indicates anagramming the letters.
'after' means one lot of letters go next to another.
'the one here' becomes 'this' (I've seen this in another clue).
'let' with letters rearranged gives 'tle'.
'tle' after 'this' is 'THISTLE'.
(Other definitions for thistle that I've seen before include "Plant with prickly-edged leaves" , "The Scottish weed?" , "Scottish flower" , "Scotland's emblem" , "Lithest (anag) - plant" .)