verb
to look up (in a book or dictionary), to look up / check (online or in a reference)
B1
Nachschlagen: to look up information in a reference (book, dictionary) or online; also 'consultar'/'check'. It’s a separable, strong (irregular) verb (schlagen→schlug; Partizip nachgeschlagen) using haben as auxiliary. Not reflexive. Commonly used with 'in' + dative: in einem Wörterbuch nachschlagen frequently.
Examples
Ich muss das Wort im Wörterbuch nachschlagen.
I need to look up that word in the dictionary.
Ich schlage das Wort im Wörterbuch nach.
I look up the word in the dictionary.
Er schlug die Bedeutung im Lexikon nach.
He looked up the meaning in the dictionary.
Details
Mnemonics
Picture flipping through a thick dictionary and putting a small 'note' (nach) on the page you found.
Sounds a bit like 'notch-slog' — imagine slogging through pages to find an entry.
Notes
Nachschlagen is a separable-prefix verb: in main clauses the prefix 'nach' separates (ich schlage das Wort nach). The past participle is 'nachgeschlagen' and uses the auxiliary 'haben'. It commonly means to consult a reference (book, dictionary, database, or the internet).