Act up on a journey, as a supporter (6)
I believe the answer is:
tripod
'a supporter' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'act up on a journey' is the wordplay.
'act' becomes 'do' (I've seen this in other clues**).
'up' is a reversal indicator (in down clue: letters go upwards).
'on' is a charade indicator (letters next to each other).
'a journey' becomes 'trip' (trip is a kind of journey).
'do' back-to-front is 'od'.
'od' after 'trip' is 'TRIPOD'.
'as' is the link.
Can you help me to learn more?
(Other definitions for tripod that I've seen before include "Stand for camera etc" , "Something on three legs" , "Drop it (anag)" , "Three-legged support" , "Three-legged stand as for camera" .)