Definition from Wiktionary, the free dictionary
false cognate (plural false cognates)
- A word that appears to be cognate to – that is, to have a shared linguistic origin with – a given word, but that is in fact unrelated.
- (sometimes proscribed) A false friend, a word that appears to have the same meaning as a given word, but that does not.
Usage notes 
- Some speakers consider the usage of false cognate to mean "false friend" to be incorrect.
- Examples of false cognates:
- Many completely unrelated languages use some variant of ma for "mother".
- English have (and the related German verb haben) and Latin habeō are thought to be false cognates — have is more likely cognate to capiō.
- French attendre and English attend are indeed cognates (they have a shared root), but they are false friends (they have different meanings), thus, they are only false cognates in the second sense.
- Similarly, Spanish atender and English attend mean "assist, look after" and "attend," respectively; while Spanish asistir and English assist mean "attend" and "assist," respectively. Both words are derived from Latin attendere.
- English island and Spanish isla are false cognates but also are true friends, since they share the same meaning. Island is derived from old English igland and isla is derived from Latin insula.