Avoid the upset of endless travel (5)
I believe the answer is:
avert
'avoid the upset' is the definition.
'avert' can be an answer for 'avoid' (synonyms). I am not certain of the 'the upset' bit.
'of endless travel' is the wordplay.
'of' is an anagram indicator (the answer comes from or 'of' the letters).
'endless' means to remove the last letter.
'travel' with its last letter taken off is 'trave'.
'trave' is an anagram of 'AVERT'.
Can you help me to learn more?
(Other definitions for avert that I've seen before include "Obviate" , "Fend off" , "Prevent from happening" , "With prominent incisors" , "Prevent from occurring" .)