Dic: mostly

[1]

1) almost entirely; chiefly
2) on many or most occasions; usually

[2]

(a) used for saying what the largest part of something is like or consists of: a group of reporters, mostly American. The panel consists mostly of local businessmen.
(b) generally: Tonight's going to be mostly cloudy.
(c) used for emphasizing the main reason or purpose of something: [mostly because] The majority said they work mostly because they need the money. [mostly for]This machine was used mostly for agricultural work.

... Collins, MacMillan English Dictionary(American)

[3]

(...)
7. In an utmost, supreme, uttermost, ultimate or maximal manner.
8. In a maximum, top, topmost, paramount or uppermost manner.theoretic]
9. In a great manner.

.... Webster's Online Dictionary