Tell engineers’ rambling tale (6)
I believe the answer is:
relate
'tell' is the definition.
(as in to tell or relate a story)
'engineers' rambling tale' is the wordplay.
'engineers'' becomes 'RE' (Royal Engineers).
'rambling' indicates an anagram.
'tale' anagrammed gives 'late'.
're'+'late'='RELATE'
(Other definitions for relate that I've seen before include "Make a logical or casual connection" , "Narrate in Tralee" , "Tell in Tralee" , "Tell (a story)" , "Show a connection between (things)" .)