One is securing trade? Credit mostly impractical (10)

I believe the answer is:

idealistic

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'impractical' is the definition.
(synonyms)

'one is securing trade? credit mostly' is the wordplay.
'one is' becomes 'II' (more than one I).
'securing' means one lot of letters goes inside another.
'trade?' becomes 'deal' ('deal' can be a synonym of 'trade').
'credit mostly' becomes 'stic' (I am not sure about this - if you are sure you should believe this answer much more).
'ii' placed around 'deal' is 'ideali'.
'ideali'+'stic'='IDEALISTIC'

Can you help me to learn more?

(Other definitions for idealistic that I've seen before include "Utopian" , "Naively impractical" , "Striving for perfection" , "High-minded - italicised (anag)" , "Seeking the best" .)

I've seen this clue in The Times.

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