On way up, encountered one couple (4)
I believe the answer is:
item
'couple' is the definition.
(a romantic couple are 'an item')
'on way up encountered one' is the wordplay.
'on way up' shows that the letters should be reversed in order.
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'one' becomes 'i' (Roman numeral).
'met'+'i'='meti'
'meti' reversed gives 'ITEM'.
(Other definitions for item that I've seen before include "pair?" , "date" , "Single unit" , "A single piece of information" , "One of a series (or a couple!)" .)