Translation:I need a dictionary to look up a word.
Yes, the literal translation would be something like "I have need of a dictionary, to search (in) it for a word". So there should be something in the English translation to indicate looking in the dictionary. The English is translated from the original French expression, not the other way around.
If I search the dictionary for the word "letter", I'll probably encounter it on the first page, in the description of A (first letter of the alphabet).
If I look up "letter", I'll open the dictionary somewhere in the middle, work my way towards the entry "letter" and I will find that "letter" has several different meanings.
Un pléonasme est une répétition, dans un même énoncé, de mots ayant le même sens. Prévoir à l'avance
Comparer entre eux
Une heure de temps
Reculer en arrière
Monter en haut
Descendre en bas
(From the app Améliorez votre français !)
Yes, a "redundancy in wording". But redundancy doesn't sound negative. If something is a pleonasm, it is by definition unnecessarily wordy, which makes it harder to follow. It's something you typically want to avoid, especially in writing. Although in some places redundancy is desirable, e.g. in speeches.
In this case, it's not exactly a pleonasm. "Un mot" implies it's "one word", while you could also need a dictionary to look up e.g. twenty words. So the second part is not really redundant. And the first part also isn't. I could also look up a word in an encyclopedia or online instead of in a dictionary.