"Sound Mind" from one Greek word, the only time it is used in the NT. Here's a run down on the etymology in scripture, at least as far as Strong's takes it.
G4995
σωφρονισμός
sōphronismos
so-fron-is-mos'
From G4994; discipline, that is, self control: - sound mind.
G4994
σωφρονίζω
sōphronizō
so-fron-id'-zo
From G4998; to make of sound mind, that is, (figuratively) to discipline or correct: - teach to be sober.
G4998
σώφρων
sōphrōn
so'-frone
From the base of G4982 and that of G5424; safe (sound) in mind, that is, self controlled (moderate as to opinion or passion): - discreet, sober, temperate.
G4982
σώζω
sōzō
sode'-zo
From a primary word σῶς sōs̄ (contraction for the obsolete σάος saos, “safe”); to save, that is, deliver or protect (literally or figuratively): - heal, preserve, save (self), do well, be (make) whole.
G5424
φρήν
phrēn
frane
Probably from an obsolete φράω phraō (to rein in or curb; compare G5420); the midrif (as a partition of the body), that is, (figuratively and by implication of sympathy) the feelings (or sensitive nature; by extension [also in the plural] the mind or cognitive faculties): - understanding.
G5420
φράσσω
phrassō
fras'-so
Apparently a strengthened form of the base of G5424; to fence or inclose, that is, (specifically) to block up (figuratively to silence): - stop.
Sounds like a combination of thoughts and emotions. Isn't that what the 'soul' is? Isn't that what 'we' are? I think all the scripture quoted relate very well to this.