Lexical Definition

‎διαστέλλομαι‎ diastéllomai (dee-as-tel'-lom-ahee) to give orders ^G:V
middle voice from ‎διά‎ and ‎στέλλω‎

charge, that which was (give) commanded(-ment).

• to set (oneself) apart (figuratively, distinguish), i.e. (by implication) to enjoin

Abbott-Smith

δια-στέλλω [in LXX for בּדל hi. (De 10:8, al.), זהר hi. (Ez 3:18, 19, al.), and 19 other words]
1. to divide, distinguish, define.
2. to command, charge expressly: pass., τὸ διαστελλόμενον, He 12:20. Mid., in late Gk. with same sense (so Ez, l.c.; et al. in LXX; MM, s.v.); a. dat. pers., Mk 8:15, Ac 15:24; seq. ἵνα, Mt 16:20, Mk 5:43 7:36 9:9.†

Abbott-Smith References

Liddell-Scott-Jones

διαστέλλω,

put asunder, expand, separate, συνεσταλμένα δ. [Refs 5th c.BC+]; δ. τι ταῖς ὄνυξι to tear it open, [Refs 1st c.AD+]:—passive, to be dilated, of the lungs or heart, [Refs 4th c.BC+]being dispersed, [Refs 4th c.BC+]; διασταλήτω πᾶσα σκοτία let all darkness be dispelled, [Refs]

__2 divide, δίχα [Refs 5th c.BC+]; distinguish, τοὺς Τρῶας τῶν Δαρδάνων [Refs 8th c.BC+]
__2.b define precisely, τὰ λεγόμενα [Refs 5th c.BC+]; intransitive, ὅρασις διαστέλλουσα distinct vision, [LXX]; also, to be distinctive, opposed to ἀπόλυτον εἶναι, [Refs 2nd c.AD+]:—middle, δ. περί τινος [Refs 5th c.BC+]:—passive, διεσταλμένος definite, determinate, [Refs 2nd c.AD+]
__3 command expressly, give express orders, ῥητῶς ὑπέρ τινος [Refs 2nd c.BC+]:—middle, [LXX+3rd c.BC+]
__4 pronounce, χείλεσι [LXX]
__5 give orders in writing, [Refs 2nd c.BC+] —more frequently in middle [Refs 2nd c.BC+]
__6 pay, render, especially in kind, [Refs 2nd c.AD+]; make an order for payment, [Refs 2nd c.AD+]; discharge a vow, [LXX]
__7 set apart, τινὰ ἑαυτῷ[LXX+3rd c.BC+]
__II intransitive, differ, πρός τινα [Refs 2nd c.BC+]

_{LSJ Scripture Refs: LXX.1Kgs.3.1 ☩ LXX.Josh.1.19 ☩ Mark.5.43 ☩ LXX.Lev.5.4 ☩ LXX.Lev.22.21}