Encountered old gymnast finally climbing pole (5)
I believe the answer is:
totem
'pole' is the definition.
(I've seen this before)
'encountered old gymnast finally climbing' is the wordplay.
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'finally' suggests the final letters.
'climbing' is a reversal indicator (in a down clue, letters climb up).
The last letter of 'gymnast' is 't'.
'met'+'o'+'t'='metot'
'metot' backwards is 'TOTEM'.
(Other definitions for totem that I've seen before include "Natural emblem of spiritual significance" , "Sort of pole" , "symbolic animal" , "family emblem" , "Primitive object of worship" .)