elision
🇺🇸
/ɪˈlɪʒn/
🇬🇧
/ɪˈlɪʒn/
When you don't pronounce a part of a word, like saying 'sith' instead of 'sixth'.
In casual speech, elision is common, as when 'for' becomes 'f' in contractions like 'gimme'.