microgroove

[mahy-kruh-groov] /ˈmaɪ krəˌgruv/
noun
1.
a needle groove so narrow that over 200 can be cut in an inch of playing surface on a long-playing record.
Origin
1945-50; micro- + groove
British Dictionary definitions for microgroove

microgroove

/ˈmaɪkrəʊˌɡruːv/
noun
1.
  1. the narrow groove in a long-playing gramophone record
  2. (as modifier): a microgroove record