Hi Sonya,
1) "Something worth little or nothing". Here shouldn't the sentence be: "Something worths little or nothing" ? Not sure if this is a complete context. It looks strange to me!
This is worth every penny! But there is no verb in your questioned “sentence”.
2) "Water pollution is caused by run-off from factories". Does run-off a synonymous for chemicals/residues ? Run off here mean “waste discharge from the factory.
We can make reference of a “snow run off” meaning water from the melting of snow.
3) Is rather than a synonymous for "instead of" ? Ex.: Rather than go out to dinner, let's just order in a pizza. => Yes, you may say that!
4) The word "chieftain" can be also written "chieftan" ? To me, It’s a proper name, not a word.
5)"Sam's grandfather grounded him by his constant bad/insulting words". Is grounded a synonymous for scolded/reprimanded ? And what is its infinitive form? Because 'ground' is the simple past and past participle forms of the verb to grind.
When a shipped is “grounded”, it means it lost its ability to sail. If your parents grounded you, you are not allowed to leave the house, this is probably accompanied by scolding and reprimanding after you break the 9 pm curfew. The infinitive form is "ground". Uusually it's used in passive voice.
You may see this on the news: American Airline grounds its entire fleet of MD 80 for wiring safety inspection