Farcical when a bus breaks down on the side of the road (6)
I believe the answer is:
absurd
'farcical' is the definition.
(thesaurus)
'a bus breaks down on the side of the road' is the wordplay.
'breaks down' indicates an anagram.
'on the side of' says to hollow out the word (remove centre letters) (I've seen 'on the side' mean this (the letters on the sides)).
'road' with its middle taken out is 'rd'.
'bus' anagrammed gives 'bsu'.
'a'+'bsu'+'rd'='ABSURD'
'when' is the link.
(Other definitions for absurd that I've seen before include "word to describe Beckett's theatre!" , "Wildly illogical" , "Arousing derision" , "Really ridiculous, silly" , "Ludicrous, silly" .)