Join one by end of esplanade (5)
I believe the answer is:
unite
'join' is the definition.
('unite' can be a synonym of 'join')
'one by end of esplanade' is the wordplay.
'one' becomes 'unit' ('unit' can be a synonym of 'one').
'by' says to put letters next to each other.
'end of' says to take the final letters.
The final letter of 'esplanade' is 'e'.
'unit'+'e'='UNITE'
(Other definitions for unite that I've seen before include "Make one" , "Join forces" , "Get together" , "Put together" , "pool resources" .)