godan verb (-su), transitive verb
Used for physically extending something by joining or adding material, or for replenishing a supply (e.g., adding liquid to a pot, coals to a fire). Often implies continuing or supplementing what is already there.
家を継ぎ足して部屋を増やした。
We extended the house and added a room.
The simmered dish was running low on liquid, so I added more broth.