Serviceman: see one at attention endlessly (5)
I believe the answer is:
vicar
'serviceman' is the definition.
(man giving church services)
'one at attention endlessly' is the wordplay.
'one' becomes 'vic' (I am not sure about this - if you are sure you should believe this answer much more).
'at' means one lot of letters go next to another.
'attention' becomes 'care' (synonyms).
'endlessly' means to look at the middle letters (the ends of the words are removed).
The middle of 'care' is 'ar'.
'vic'+'ar'='VICAR'
'see' acts as a link.
Can you help me to learn more?
(Other definitions for vicar that I've seen before include "Cleric" , "See stand-in" , "Serviceman" , "Member of the clergy" , "Minister" .)