Advertising, say, 'Fashionable woolly, sturdy with navy top'? (7,8)

'advertising' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.

''fashionable woolly sturdy with navy top'?' is the wordplay.
''fashionable' becomes 'in' (in can mean fashionable or trendy).
'woolly' is an anagram indicator (I've seen this in other clues).
'with' says to put letters next to each other.
'navy top'?' becomes 'service' (I can't justify this - if you can you should give a lot more credence to this answer).
'sturdy' is an anagram of 'dustry'.
'in'+'dustry'='industry'
'industry' put after 'service' is 'SERVICE INDUSTRY'.

'say' is the link.

Can you help me to learn more?