PSYCHROMETER Psy*chrom"e*ter, n. Etym: [Gr. psychro`s cold + -meter: cf. F. psychromètre.]
Defn: An instrument for measuring the tension of the aqueous vapor in the atmosphere, being essentially a wet and dry bulb hygrometer.
PSYCHROMETRICAL
Psy`chro*met"ric*al, a.
Defn: Of or pertaining to the psychrometer or psychrometry.
PSYCHROMETRY
Psy*chrom"e*try, n.
Defn: Hygrometry.
PSYLLA
Psyl"la, n.; pl. Psyllæ. Etym: [NL., from Gr. (Zoöl.)
Defn: Any leaping plant louse of the genus Psylla, or family
Psyllidæ.
PTARMIGAN Ptar"mi*gan, n. Etym: [Gael. tarmachan; cf. Ir. tarmochan, tarmonach.] (Zoöl.)
Defn: Any grouse of the genus Lagopus, of which numerous species are known. The feet are completely feathered. Most of the species are brown in summer, but turn white, or nearly white, in winter.