| opener(cause, source, origin, derivation, birth) |
| opening(cause, foundation, basis) |
| originating point(expression, idiom) |
| origination(cause, source, foundation, basis, origin) |
| originator(person, cause, foundation, basis, spring) |
| outbreak(cause, source, origin, derivation, birth) |
| outset(cause, start, beginning, source, origin) |
| parentage(cause, influence, source, derivation, ancestry) |
| paternity(cause, foundation, basis) |
| percolate |
| person |
| pit(noun, supply, reserve, source, bore) |
| pithead(noun, pit, excavation, coalfield, coalmine) |
| producer(cause, source, derivation) |
| radiation source(expression, idiom) |
| reserve(noun, supply, deposit, pit, excavation) |
| rising(cause, foundation, basis) |
| river headwaters(expression, idiom) |
| roots(cause, influence, source, derivation, ancestry) |
| rootstock(noun, origin) |