No, you do not "know" that "olam" means eternal. That is what you choose to believe because it lines up with your denominational teachings. OTOH I have supported my posts with a quote from the Brown Driver Briggs Hebrew lexicon to say nothing of the individual study I did. Here are the first 10 our of 48. Note 4, 6, 7 and 8 God Himself is speaking. I hope God did not get it wrong.
(14) I know that, whatsoever God doeth, it shall be for ever: [עולם] nothing can be put to it, nor any thing taken from it: and God doeth it, that men should fear before him.
(28) For the LORD loveth justice, and forsaketh not His saints; they are preserved for ever; [עולם] but the seed of the wicked shall be cut off.
(17) (45:18) I will make thy name to be remembered in all generations; therefore shall the peoples praise thee for ever and ever. [לעלם ועד]
(6) Lift up your eyes to the heavens, and look upon the earth beneath; for the heavens shall vanish away like smoke, and the earth shall wax old like a garment, and they that dwell therein shall die in like manner; but My salvation shall be forever, [עולם] and My favour shall not be abolished.
(13) Instead of the thorn shall come up the cypress, and instead of the brier shall come up the myrtle; and it shall be to the LORD for a memorial, for an everlasting [עולם] sign that shall not be cut off.
(5) Even unto them will I give in My house and within My walls a monument and a memorial better than sons and daughters; I will give them an everlasting [עולם] memorial, that shall not be cut off.
(40) and I will bring an everlasting [עולם] reproach upon you, and a perpetual [עולם] shame, which shall not be forgotten.
(40) And the whole valley of the dead bodies, and of the ashes, and all the fields unto the brook Kidron, unto the corner of the horse gate toward the east, shall be holy unto the LORD; it shall not be plucked up, nor thrown down any more for ever. [עולם]
(5) They shall inquire concerning Zion with their faces hitherward: 'Come ye, and join yourselves to the LORD in an everlasting [עולם] covenant that shall not be forgotten.'
(39) With their poison I will prepare their feast, and I will make them drunken, that they may be convulsed, and sleep a perpetual [עולם] sleep, and not wake, saith the LORD.