Native American mostly adopting expert methodology (8)
I believe the answer is:
approach
'methodology' is the definition.
(thesaurus)
'native american mostly adopting expert' is the wordplay.
'native american' becomes 'Apache' (group of Native American tribes).
'mostly' means to remove the last letter (most but not all of the word).
'adopting' indicates putting letters inside (inserted letters are taken on or adopted).
'expert' becomes 'pro' (short for professional).
'apache' with its final letter removed is 'apach'.
'apach' going around 'pro' is 'APPROACH'.
(Other definitions for approach that I've seen before include "initial proposal" , "Speak to" , "attitude" , "Drae near" , "golf shot" .)