Friendly exclusive about one in taxi (8)
I believe the answer is:
sociable
'friendly' is the definition.
(synonyms)
'exclusive about one in taxi' is the wordplay.
'exclusive' becomes 'sole' (synonyms).
'about' indicates putting letters inside.
'one' becomes 'I' (Roman numeral).
'in' indicates putting letters inside.
'taxi' becomes 'cab' (synonyms).
'i' going inside 'cab' is 'ciab'.
'sole' going around 'ciab' is 'SOCIABLE'.
(Other definitions for sociable that I've seen before include "Fond of mixing with others" , "Friendly and pleasant" , "Fond of others' company" , "Companionable, friendly" , "Easy in company" .)