Remember my post on any more or anymore? This one came up in the same conversation, but of course, English being as it is, the answer is slightly different.

The question: is it some time or sometime?

Sometime is only used as an adjective or adverb – i.e. a word describing the attributes of a noun or one that modifies the meaning of a verb, adjective or other adverb. So “Her sometime adversary, Bettina, had moved away and was no longer part of the Scrabble club”. But do look at my post on erstwhile or sometime for more detail here.

Some time is used in all other cases – “Jerry spent some time choosing the word to place on the board”.

Sometimes is an adverb meaning occasionally. “Sometimes he went to the cinema in the city; sometimes he preferred the local one”. Compare “My sometime friend, Bettina” with “My sometimes friend, Bettina” – the former implies that they were once friends, the latter that they were friends and weren’t friends at different times.

To use them both together “Her sometime very closest friend spent some time in Arizona before she got back in touch”.

You can find more troublesome pairs here and the index to them all so far is here. And I look at sometime or ertswhile here!