tell him
tell 'im
/ˈtɛlɪm/ElisionLinking
What happens to the sounds
The h in unstressed him disappears and the word sticks to the previous one: tell him → “TELL-im”.
When to use it
Same with love 'im, ask 'im. The h comes back when him is stressed (tell HIM, not her).
Casual → formal
Slang
tell 'im
Neutral
tell him
Sound notes
Elision: a sound disappears completely (often t, v, h or th).