Today, people want to consult dictionaries of good quality, but they expect them to be available online for free. For this reason, publishers need advertisements to cover the costs of producing and maintaining online dictionary content. This paper aims to investigate the role of advertisements in language reception, production, and learning following online dictionary consultation. It also undertakes to determine whether advertisements in an online dictionary affect the time needed for dictionary-based decoding and encoding. In the experiment, participants consulted one of the most prestigious dictionaries of English for foreign learners, OALD9 (Oxford Advanced Learner’s Dictionary, 9th edition). Two versions of the dictionary were employed in the study: one that includes advertisements and is available online free of charge, and its advertisement-free counterpart, OALD9 Premium. In the receptive task, the participants were requested to explain the meaning of new English words. In the productive one, they had to use the words in sentences. Meaning retention was checked in the immediate post-test. The research reveals that advertisements in OALD9 impede language reception, production, and learning, and also extend the time for comprehending new words. Suggestions for further research into advertisements on dictionary websites are presented in the final part of the paper.