Write promissory note about the end of June (3)
I believe the answer is:
pen
'write' is the definition.
(I know that write can be written as pen)
'promissory note about the end of june' is the wordplay.
'promissory note' becomes 'pn' (this might be a standard abbreviation I've not previously seen).
'about' means one lot of letters goes inside another.
'the end of' suggests the final letters.
The last letter of 'june' is 'e'.
'pn' going around 'e' is 'PEN'.
Can you help me to learn more?
(Other definitions for pen that I've seen before include "Write" , "Cage - bird" , "Writing instrument" , "Animal enclosure" , "'The ... is mightier than the sword'" .)