Vineyard obstructing second microscopic examination (8)
I believe the answer is:
scrutiny
'examination' is the definition.
(synonyms)
'vineyard obstructing second microscopic' is the wordplay.
'vineyard' becomes 'cru' (I've seen this before).
'obstructing' means one lot of letters goes inside another (inserted letters interrupt or obstruct the word).
'second' becomes 's' (common abbreviation).
'microscopic' becomes 'tiny' (I've seen this before).
's'+'tiny'='stiny'
'cru' placed within 'stiny' is 'SCRUTINY'.
(Other definitions for scrutiny that I've seen before include "From close inspection" , "Detailed perusal" , "A careful look or examination" , "City runs (anag.)" , "Close survey" .)