1. In an exhaustive manner
   "we searched the files thoroughly"
   - exhaustively 
2. Completely and absolutely ('good' is sometimes used informally for 'thoroughly')
   - soundly, good

See also: thorough

• hold open
• hold still for
• hold sway
• hold the line
• hold tight
• hold water
• hold your horses
• hold-down
• holdall
• holder
• holdfast
• holding
• holding cell
• holding company
• holding device
• holding paddock
• holding pattern
• holding pen
• holding yard
• holdout
• holdover
• holdup
• holdup man
• hole
• hole card