The plant uncle has to look out for (6)
I believe the answer is:
sesame
'the plant' is the definition.
(sesame is a kind of plant)
'uncle has to look out for' is the wordplay.
'uncle' becomes 'sam' (Uncle Sam is an example).
'has' says to put letters next to each other.
'to look' becomes 'see'.
'out' means to remove the last letter.
'for' becomes 'e' (I can't justify this - if you can you should believe this answer much more).
'see' with its last letter taken off is 'se'.
'sam' put after 'se' is 'sesam'.
'sesam'+'e'='SESAME'
Can you help me to learn more?
(Other definitions for sesame that I've seen before include "Oil-rich seed plant" , "Opening word for the oilplant?" , "Open .... is a pantomime cry" , "'Open . . . . . .'' is a magic phrase to gain access" , "said to be effective in opening spell" .)