Rashi on Deuteronomy 23:14/רש"י על דברים כ״ג:י״ד

1על אזנך [AND THOU SHALT HAVE A PIN] על אזנך — i.e. besides (על, “in addition to”, not “upon”) your other implements.

2אזנך has the same meaning as זין in the phrase כלי זין.