pre-noun adjectival
unexpected; unseasonal; untimely
Pre-noun adjectival (rentaishi) meaning something happening at an unexpected time or out of season. Often used with nouns like 雨, 雪, 客, 出来事. The glosses 'unthought of' and 'unscheduled' are less common; 'unexpected' and 'unseasonal' cover the main uses.
I got caught in an unexpected rain and was soaked.
An unseasonal snow whitened the garden.
Compound of 時 (とき, 'time') + ならぬ (archaic negative of なり, 'to be'), literally 'not being the time'. The exact historical derivation is uncertain, but it functions as a fixed literary expression.