reklamo

The re- you can see is not the re- you know. Esperanto really does have a productive prefix re-, meaning again or back: revidi to see again, reveni to come back, redoni to give back. So reklamo invites you to split it, and then leaves you holding klamo, which is not a word in the language and never has been. The split fails, and the word has to be learnt whole.

What makes it a gift rather than a trap is that Latin agrees with you. Reclamare genuinely is re- plus clamare, to shout - to shout back, to cry out against something. That is where English "reclaim" and "clamour" come from too. So the instinct is right about the history and wrong about the language: the seam was cut in Latin, the halves fused there, and Esperanto imported the finished word. It belongs with inspiri and konsterni in that class, and knowing the Latin still helps you remember it even though it gives you no rule you can reuse.

Advertising, not complaint. The commercial meaning arrived via French réclame in the nineteenth century, which is the sense Esperanto has. A reklamo is a single advertisement - in a paper, on a wall, on the television - and the mass noun advertising as an activity. The verb is reklami (to advertise), and note the object: you reklamas the product, not the customer. Keep it apart from anonci, to announce, which is neutral: a station anoncas a train, a company reklamas its wares. Reklamilo is the poster or leaflet, reklamisto the advertiser, and reklamejo the hoarding it all goes on.