Green’s Dictionary of Slang

1. (US campus) a sober, religious student.

1856

B.H. Hall College Words (rev. edn) 298: long-ear [...] a student of a sober or religious character.

2. (US) an eavesdropper; thus have long ears, to eavesdrop.

1935		in DARE .
1935		M. Sandoz Old Jules 264: He talks everything out and she has long ears [DARE].
1942		Berrey & Van den Bark Amer. Thes. Sl.