“What did you do this weekend?” “I worked in the yard, 'mostly'.” [=I spent most of my time working in the yard]
The people at the concert were 'mostly' older people. [=most of the people were older people]
He gets around 'mostly' [='mainly, chiefly'] by car. [=he usually uses a car to get around]
(..) and I've no help to give you. Oh, Scarlett, l... ...l'm a coward. You, Ashley, a coward? What are you afraid of? Oh, mostly of life becoming too real for me, I suppose. Not that I mind splitting rails... ...but I do mind very much losing the beauty of that life I loved. (..)1939 Gone with the Wind
(..) Miss Melly, she done had her baby today. And a fine baby boy... ...and Miss Scarlett and me, we brung him. Do you mean to tell me that Scarlett-- Well, it was mostly me, Cap'n Butler, only Miss Scarlett... ...she helped me a little, but I don't expect no doctor could have done no better! (..)1939 Gone with the Wind