One new drink I had is flavourless (7)
I believe the answer is:
insipid
'is flavourless' is the definition.
(synonyms)
'one new drink i had' is the wordplay.
'one' becomes 'i' (Roman numeral).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'drink' becomes 'sip' (sipping is a kind of drinking).
'i had' becomes 'i'd' (contraction).
'i'+'n'+'sip'+'id'='INSIPID'
(Other definitions for insipid that I've seen before include "Bland, flavourless" , "Very weak" , "Colourless" , "Jejune" , "Lacking 10" .)