Ahem and Hello

Ahem noun - The utterance of a sound similar to clearing the throat; intended to get attention, express hesitancy, fill a pause, hide embarrassment, warn a friend, etc..

Hello and ahem are semantically related in emphatic exclamation topic. In some cases you can use "Hello" instead a noun "Ahem".

Hello noun - An expression of goodwill upon meeting.

Ahem and hello are semantically related in boo topic. You can use "Ahem" instead a noun "Hello", if it concerns topics such as wow.