Lexical Definition

‎μεγαλεῖος‎ megaleîos (meg-al-i'-os) mighty ^G:A
from ‎μέγας‎

great things, wonderful works.

• magnificent, i.e. (neuter, plural as noun) a conspicuous favor, or (subjectively) perfection

Abbott-Smith

μεγαλεῖος, -εία, -εῖον (< μέγας), [in LXX: Ps 70 (71):19* (גָּדוֹל), al., freq. in Sir;]
magnificent, splendid (Xen., Plut., al.): Ac 2:11.†

Abbott-Smith References

Liddell-Scott-Jones

μεγαλεῖος-ος, α, ον,

(μέγας) magnificent, splendid, ῥήματα [Refs 5th c.BC+]; κτῆμα[Refs 5th c.BC+]; πίστιν -οτάταν probably in Paean cited in [Refs 1st c.AD+]; τὸ μ. τῶν πράξεων, τῆς ἀθανασίας, [Refs 2nd c.BC+], cf. Vett. Val.70.1; τὰ μ. mighty works, [LXX+NT]. adverb -ως greatly, ὠφελῶν τὴν πόλιν [Refs 5th c.BC+]; magnificently, μ. εἴρηκας [Refs 5th c.BC+]: comparative -ότερον [Refs 5th c.BC+]; -οτέρως, γαμεῖν [Refs 5th c.BC+]

__2 of persons, stately, haughty, [Refs]
__3 τὸ μ. τινός, as a title, Highness, [Refs 3rd c.AD+]
__4 of style, elevated, [Refs 4th c.BC+] adverb superlative -ότατα, ἑρμηνεῦσαι [Refs 2nd c.AD+]

_{LSJ Scripture Refs: LXX.Deut.11.2 ☩ Acts.2.11}