A chum married Nimby, for one (7)
I believe the answer is:
acronym
'nimby for one' is the definition.
I can't judge whether this defines the answer.
'a chum married' is the wordplay.
'chum' becomes 'crony' (synonyms).
'married' becomes 'm'.
'a'+'crony'+'m'='ACRONYM'
Can you help me to learn more?
(Other definitions for acronym that I've seen before include "A word formed from the initial letters of others" , "Word made from initial letters of other words" , "Ernie, for one" , "My acorn may generate a new word from first letters" , "Word such as radar, laser" .)