An upright supporter (4)
I believe the answer is:
mast
This clue might be a double definition.
'an upright' is the first definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's a link between them I don't understand?
'supporter' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for mast that I've seen before include "Nautical pole" , "Television transmitter" , "Supporting pole, for radio aerial, perhaps" , "Vertical spar for supporting sails etc" , "Large transmitter" .)