a manager; a barkeeper, a landlord (of a pub); a storekeeper, shopkeeper; an owner / a master (a person with a master's degree) / a master's degree / a master (a person in charge; a skilled person)

to master (to acquire complete knowledge or skill (in something))

start

a start

start! begin!

woman

bed sheet

(baseball) slider / slider of a zipper / slider (sandwich)

slate

world