Once, Pole travelled around river with king and Columbus, for example (8)
I believe the answer is:
explorer
'columbus for example' is the definition.
(columbus is a kind of explorer)
'once pole travelled around river with king' is the wordplay.
'once' becomes 'ex' (prefix meaning former or onetime).
'travelled' indicates anagramming the letters.
'around river' becomes 'r' (abbreviation for river. I am not sure about the 'around' bit.).
'with' is an insertion indicator.
'king' becomes 'R' (abbreviation for rex, king in Latin).
'pole' with letters rearranged gives '[pole]'.
'[pole]'+'r'='ploer'
'ploer' placed around 'r' is 'plorer'.
'ex'+'plorer'='EXPLORER'
'and' is the link.
Can you help me to learn more?
(Other definitions for explorer that I've seen before include "Stanley and Livingston, say" , "Investigative traveller" , "Adventurer in little-known regions" , "Shackleton or Amundsen, say" , "One carrying out system-atic investigations" .)