Returning in a public vehicle one tabloid shows a cocktail (9)
I believe the answer is:
Here is my best explanation:
'a cocktail' is the definition.
(margarita is a kind of cocktail)
'returning in a public vehicle one tabloid' is the subsidiary indication.
'returning' shows that the letters should be reversed in order.
'in' means one lot of letters goes inside another.
'public vehicle' becomes 'tram' (I've seen this before).
'one' becomes 'i' (roman numeral).
'tabloid' becomes 'rag' ('rag' can be a synonym of 'tabloid').
'atram' enclosing 'irag' is 'atiragram'.
'atiragram' in reverse letter order is 'margarita'.
'shows' is the link.
(Other definitions for margarita that I've seen before include "Tequila-based cocktail", "Cocktail consisting of tequila and lemon juice", "Spanish girl", "Stiff drink", "Type of tequila cocktail", "Tequila/citrus cocktail", "Tequila and lime cocktail" and "Caribbean island".)