Teachers meeting with old actor: that bears fruit (3-4)
I believe the answer is:
nut-tree
'that bears fruit' is the definition.
(type of tree)
'teachers meeting with old actor' is the wordplay.
'teachers meeting' becomes 'nut' (National Union of Teachers).
'with' means one lot of letters go next to another.
'old actor' becomes 'tree' (19th-century actor Herbert Beerbohm Tree).
'nut'+'tree'='NUT-TREE'
(Other definitions for nut-tree that I've seen before include "Hazel, say" , "Possible source of Brazil" .)