Five experiments were designed to examine whether subjects attend to different aspects of meaning for familiar and unfamiliar words. In Experiments 1-3, subjects gave free associations to high-and low-familiarity words from the same taxonomic category (e.g., seltzer:sarsparilla; Experiment 1), from the same noun synonym set (e.g., baby:neonate; Experiment 2), and from the same verb synonym set (e.g, abscond:escape; Experiment 3). In Experiments 4 and 5, subjects first read a context sentence containing the stimulus word and then gave associations; stimuli were novel words or either high-or low-familiarity nouns, Low-familiarity and novel words elicited more nonsemantically based responses (e.g, engram:graham) than did high-familiarity words. Of the responses semantically related to the stimulus, low-familiarity and novel words elicited a higher proportion of definitional responses [category (e.g., sarsparilla:soda), synonym (e.g., neonate:newborn), and coordinate (e.g., armoire: dresser)), whereas high-familiarity stimuli elicited a higher proportion of event-based responses [thematic (e.g., seltzer:glass) and noun:verb (e.g., baby:cry)]. Unfamiliar words appear to elicit a shift of attentional resources from relations useful in understanding the message to relations useful in understanding the meaning of the unfamiliar word.To understand Sentence I, one must understand the thematic relations of salmon, sturgeon, or brans ion to the verb catch and its agent sportsman. This understanding must be related to knowledge about the practices of sports fishermen to understand the event described in the sentence. I will refer to semantic relations between words linked by an event (e.g., salmon:sportsman, and salmon: catch in Sentence I) as event-based relations. If Sentence I contains a familiar word, salmon, then the reader's task is simply to understand the proposition expressed, information carried largely by event-based relations. On the other hand, if Sentence I contains an unfamiliar word, sturgeon, or a novel word, bransion, then the reader has the additional task of inferring what kind of thing a sturgeon or a bransion is. The reader must infer that a bransion is a kind of fish. I will refer to semantic relations that answer the question, "What kind of thing is it?" (e.g., bransion:fish and salmon:fish) as definitional relations. If Sentence I contains a novel word, then the reader must try not only to understand the proposition expressed but to infer a definitional relation between bransion and some familiar concept, such asfish.The task of understanding a proposition and the task of inferring the meaning of an unfamiliar word may call on somewhat different sets of semantic relationships. One possibility is that people will pay more attention to definitional relations for unfamiliar words than for familiar words. According to this definition hypothesis, the most People are continually learning the meanings of new words. Most are picked up casually from the context, without the help of a formal definition (Jenkin...