Translation:I looked up that word in a dictionary right away.
8 months later, I actually get it.
To say "I consult a dictionary", you say 辞書を引く (jisho o hiku), where the dictionary is the object of the verb. When you want to specify what you're looking up, you say ～を辞書で引く (~ o jisho de hiku). The dictionary is the means you use to look something up, so the thing you are looking up becomes the direct object (marked by を) rather than the dictionary.
It actually means, "That word I looked up in a dictionary right away." は makes "That word" the topic of the sentence. This goes against some English speakers sensibilities though (breaking SVOCC rule, as if you're trying to employ two grammatical subjects). Another way to do it is to use stress or intonation to emphasize "that word" and by so doing deemphasizes the subject as in, "I looked up that word in a dictionary right away." This looks nicer in written form with these fancy italics. You could make it, "It's that word (that/which) I looked up in a dictionary right away." That would back-translate to, "すぐに辞書に引いたのは・がその言葉です。" Hey I tried . . .