build up

verb

To erect; to construct.
“Near-synonym: build out”
“The motor bogies are built up from plates and rolled sections, and have cast-steel, one-piece axleguards, with manganese liners.”
To close up by building.
“to build up a door”
To accumulate: to increase incrementally or continually.
“Ever since the secretary left, the letters in my inbox have started to build up.”
“The first English Electric units were not fitted with an anti-slip brake, but a hurried consultation of the wiring diagram showed that it should be possible to hold in the low-voltage anti-slip relay for long enough to let speed build up without cutting off the motor current.”
To strengthen.
“They had to build up their fortress to protect against attack.”
“"It took it out of me, though. I'm a rag this morning." "They work you too hard, dear. I'll take you to Margate and build you up." "Well, maybe at Easter we could do a week."”
In solitaire card games, to place a card over another card of lower value. (e.g., place 5♦ over 4♣)