adverbial none rare casualwritten
only once in a while
Builds on しかない
A full written guide for only once in a while is on the way.
This point is mapped in the grammar Path, but its examples, formation table and usage notes haven't been written yet. The fastest way to learn it now is to meet it in real sentences inside Jengo.
See this grammar in real sentences
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Study it in JengoSources Compiled with reference to A Dictionary of Advanced Japanese Grammar. Editorial confidence: low.