Riddle of second coach (8)
I believe the answer is:
strainer
'riddle' is the definition.
(thesaurus)
'second coach' is the wordplay.
'second' becomes 's' (common abbreviation).
'coach' becomes 'trainer' (I've seen this before).
's'+'trainer'='STRAINER'
'of' acts as a link.
(Other definitions for strainer that I've seen before include "Filter, sieve" , "something for tea" , "one that stretches?" , "One trying very hard" , "Sieve, colander, etc" .)