To be able to (do s.t.), to happen to (do s.t.).
Abilitative / circumstantial affix in single-argument and antipassive clauses. With roots that occur normally unaffixed it is tapa-; with roots that normally take the nasal prefix it is tapaN-.
I was able to buy fish earlier.
I was not able to do my laundry because I had no soap.
I happened to meet people on the road.
He was able to get birds earlier.
He happened to kill a dog.