Ridiculous way muscles bend at the top (6)
I believe the answer is:
absurd
'ridiculous' is the definition.
(synonyms)
'way muscles bend at the top' is the wordplay.
'way' becomes 'rd' (short for road).
'muscles' becomes 'abs' (short for abdominals).
'bend' becomes 'U' (a U-bend is a kind of bend - pipe under sink).
'at the top' says to put letters next to each other (in a down clue, some letters go above others).
'abs'+'u'='absu'
'rd' after 'absu' is 'ABSURD'.
(Other definitions for absurd that I've seen before include "Wildly illogical" , "Arousing derision" , "Highly illogical" , "Quite ridiculous, silly" , "'Ridiculous, silly (6)'" .)