Lexical Definition

‎σιωπάω‎ siōpáō (see-o-pah'-o) be quiet ^G:V
from (silence, i.e. a hush

dumb, (hold) peace.

• properly, muteness, i.e. involuntary stillness, or inability to speak
• and thus differing from ‎σιγή‎, which is rather a voluntary refusal or indisposition to speak, although the terms are often used synonymously)
• to be dumb (but not deaf also, like 2974 properly)
• figuratively, to be calm (as quiet water)

Abbott-Smith

σιωπάω, -ῶ (< σιωπή, silence) [in LXX for חשׁה, חרשׁ hi., etc. ;]
to be silent or still, keep silence: Mt 20:31 26:63, Mk 3:4 9:34 10:48 14:61, Lk 19:4 , Ac 18:9; of one dumb, Lk 1:20 (cf. IV Mac 10:18); addressed rhetorically to the sea, σιώπα, Mk 4:39.†
SYN.: ἡσυχάζω, σιγάω (q.v.).

Abbott-Smith References

Liddell-Scott-Jones

σιωπάω-άω,

infinitive σιωπᾶν [Refs 8th c.BC+]future -ήσομαι in early writers, [Refs 5th c.BC+] later -ήσω [Refs 4th c.BC+]: aorist (ἐ) σιώπησα [Refs 8th c.BC+]: perfect σεσιώπηκα [Refs 5th c.BC+]:—middle and passive, see below: Doric dialect σωπάω (which see):—keep silence, σιωπᾶν λαὸν ἀνώγει [Refs 8th c.BC+]; φησὶν σιωπῶν his silence is an admission, [Refs 5th c.BC+]; σ. τινί keep silence for or at the behest of.. , [Refs 5th c.BC+]hush! be still! [Refs 5th c.BC+]

__2 of bees, to be still, opposed to βομβέω, [Refs 4th c.BC+]
__II transitive, keep secret, speak not of, τὰ δίκαια [Refs 5th c.BC+]:—passive, ἂν σιωπηθῇ τὰ παρὰ τῶν πολεμίων [Refs 5th c.BC+]; τί σιγῶσ᾽ ὧν σιωπᾶσθαι χρεώ; [Refs 5th c.BC+]
__III middle, silence, σιωπησάμενος τὰ πλήθη [Refs 2nd c.BC+]