Emily Dickinson Lexicon

PERCH, n.² [Fr. perche; L. pertica; W. perc; Arm. perchen; probably allied to the former word in the sense of sharpness, shooting or extending. See Perk.]

1. A pole; hence, a roost for fowls, which is often a pole; also, any thing on which they light.
2. A measure of length containing five yards and a half; a rod. In the popular language of America, rod is chiefly used; but rod, pole, and perch, all signifying the same thing, may be used indifferently.