Sometime means at an unstated point in time. Come round sometime, sometime next week, sometime in the spring.
It is deliberately vague, which is why sometime soon is a promise of nothing. Written as two words, some time means a quantity of time — it took some time — and the difference is real. Sometime also means former: the sometime chairman. Note sometimes, meaning occasionally, which is a third word again.
1adverbsometimeAt an unstated point in time.
“Let's meet for coffee sometime next week.”
2adverbformerFormer, before a title.
“Her grandfather, a sometime sailor and fisherman, told wonderful stories.”
Too few real examples of this word to estimate which sense is commonest.
sometime is an indefinite time.
Middle English somtyme is some plus time. Sometimes was formed from it with the adverbial -s.
Middle English
somtyme
English, today
sometime
From Middle English somtyme, som time, some tyme, sume time, sumtym, sumtyme, equivalent to some + time.
Etymology from Wiktionary, CC BY-SA