Strong's #389: 'ak (pronounced ak)
 akin to 403; a particle of affirmation, surely; hence (by limitation) only:--also, in any wise, at least, but, certainly, even, howbeit, nevertheless, notwithstanding, only, save, surely, of a surety, truly, verily, + wherefore, yet (but).
Brown-Driver-Briggs Hebrew Lexicon:
 
  'ak 
 
 1) indeed, surely (emphatic)
 2) howbeit, only, but, yet (restrictive)
 
  Part of Speech: adverb 
Relation: akin to H403
Usage:
This word is used 160 times:
Lamentations 2:16: "the teeth: they say, We have swallowed her up:  certainly this is the day that we looked for;"
Lamentations 3:3: " Surely against me is he turned; he turneth his hand against me all the day."
Ezekiel 46:17: "his to the year of liberty; after it shall return to the prince:  but his inheritance shall be"
Hosea 4:4: " Yet let no man strive, nor reprove another: for thy people"
Hosea 12:8: "And Ephraim said,  Yet I am become rich, I have found me out substance: in all my labors"
Hosea 12:11: "Is there iniquity in Gilead?  surely they are vanity: they sacrifice bullocks in Gilgal;"
Jonah 2:4: "I am cast out of thy sight;  yet I will look again toward"
Zephaniah 1:18: "by the fire of his jealousy: for he shall make  even a speedy riddance of"
Zephaniah 3:7: "I said,  Surely thou wilt fear me, thou wilt receive instruction; so their dwelling should not be cut off,"
Zechariah 1:6: " But my words and my statutes, which I commanded my servants the prophets,"