Lexical Definition

‎אָכֵן‎ ʼâkên (aw-kane') surely ^H:Adv
from ‎כּוּן‎ (compare ‎כֵּן‎)

but, certainly, nevertheless, surely, truly, verily.

• firmly
• figuratively, surely
• also (advers.) but

1) surely, truly, indeed
1a) truly, indeed (strong assertive force)
1b) but indeed, but in fact (emphasizing a contrast)

See Greek: ὄντως · οὗτος · οὗτος · πλήν

Brown-Driver-Briggs

‎אָכֵן‎ (perhaps from ‎אַח‎; compare Aramaic ‎דֵּח‎ & ‎דִּכֵּן‎) adverb with strong asseverative force:
a. surely, truly, especially at beginning of a speech (stronger & more decided than ‎אַח‎) Gen 28:16; Exod 2:14; 1Sam 15:32; Isa 40:7; Isa 45:15; Jer 3:23 (twice in verse); Jer 4:10; Jer 8:8. In 1Kgs 11:2 ‎אָבֵן‎ stands unusually; and ‎פֶּןֿ‎ (compare ᵐ5 ᵑ6 ᵑ7) should probably be read (so Klo).
b. emphasizing a contrast, but indeed, but in fact, especially after ‎אָמַרְתִּי‎ I said or thought, expressing the reality, in opposed to what had been wrongly imagined, Isa 49:4b (opposed to v^a) Isa 53:4 (opposed to vIsa 53:3 end) Jer 3:20 (opposed to the expectation vJer 3:19 b) Zeph 3:7b Ps 31:23*b (opposed to vPs 31:23*a) Ps 66:19; Ps 82:7 (opposed to vPs 82:6) Job 32:8 (opposed to vJob 32:7).

Brown-Driver-Briggs References