Advocate in Teheran dances holding date (8)
I believe the answer is:
adherent
'advocate' is the definition.
(I've seen this before)
'teheran dances holding date' is the wordplay.
'dances' indicates anagramming the letters.
'holding' is an insertion indicator.
'date' becomes 'd' (common abbreviation eg in DOB, date of birth).
'teheran' anagrammed gives 'aherent'.
'aherent' placed around 'd' is 'ADHERENT'.
'in' acts as a link.
(Other definitions for adherent that I've seen before include "Loyal follower - sticks close" , "Supporter, fan" , "Devotee" , "Weep" , "sticker" .)