The website vocabulary.com says that extended means:
extended (adj.) beyond the literal or primary sense
So I suppose there are two ways a word could have an extended meaning:
- the word could be used in a figurative sense, rather than a literal sense
- the word could have a secondary meaning that we don’t immediately associate with the word
As for your exercise, the word mouth seems easy. People have a mouth, and so od lions – but rivers have a mouth as well.
The mouth of the Rhine is at Hoek van Holland by the North Sea.
As for a word like angry, we only need to consult a good dictionary for ideas. From Wordnik:
- adj. Displaying or feeling anger.
- Inflamed and painful.
- Dark and stormy, menacing.
That third one looks like an extended meaning to me. So, we might say:
When Stella noticed the angry clouds, she called her children inside.
The word train has dozens of meanings, so it’s a little harder to figure out which ones are the “primary” definitions and which might the “extended” meanings. But I will say this about the noun train: a railroad yard has a train, but so does a wedding dress. Moreover, about the verb train: a woman might train a dolphin, but she also might train her hair.