One seen at dusk endlessly following sun stroke (7)
I believe the answer is:
solidus
'stroke' is the definition.
(synonyms)
'one seen at dusk endlessly following sun' is the wordplay.
'one' becomes 'i' (Roman numeral).
'seen at' means one lot of letters go next to another.
'endlessly' means to remove the last letter.
'following' is a charade indicator (letters next to each other).
'sun' becomes 'sol' (Latin for 'sun').
'dusk' with its last letter removed is 'dus'.
'i' put next to 'dus' is 'idus'.
'idus' after 'sol' is 'SOLIDUS'.
(Other definitions for solidus that I've seen before include "old coin" , "Slash symbol" , "Oblique stroke, slash" .)