This inquiry examined factors that determine the knowledge of L2 words with orthographic neighbours in L1 (cognates and false cognates). 150 Polish learners of English were asked to translate 105 English cognates, false cognates and non-cognate words into Polish, and to assess the confidence of each translation. The study concludes how cross-linguistic formal similarity affects L2 word learnability, proposing a mechanism by which cognates and false cognates are acquired.