Unruffled before the start of trade function (5)
I believe the answer is:
event
'function' is the definition.
(I've seen this before)
'unruffled before the start of trade' is the wordplay.
'unruffled' becomes 'even' (I've seen this in another clue).
'before' means one lot of letters go next to another.
'the start of' indicates taking the first letters.
The first letter of 'trade' is 't'.
'even'+'t'='EVENT'
(Other definitions for event that I've seen before include "Item in sports programme" , "'Occurrence, occasion (5)'" , "pole vault maybe" , "Affair" , "Anything which happens" .)