From Proto-Eastern Polynesian *a-popo from Proto-Oceanic *qa-boŋi-boŋi (cognate with Tahitian apopo, Tongan apō) affixing *boŋi-boŋi (“early morning”) (cognates with Samoan pogipogi (“dawn, dusk, twilight”) and Tongan pongipongi (“morning, tomorrow”) – doublet of pongipongi “dim, of low light, dawn”) reduplicate of *boŋi thus doublet of pō – see there for more details.