is a mouthful
Something that is a mouthful is difficult to say or pronounce or just too long to bother saying.
Example: The new hospital is going to be called the Marjorie Jackson Nelson Hospital, which is quite a mouthful
Here built is the past participle of the irregular verb build. Follow the link to find out more and to listen to examples.
more information: build
came into operation
started working
a hell of a lot
a large amount
Example: I've got a hell of a lot of work to do.
show our locomotives off
To show off something is to display it proudly.
Example: My wife showed off the baby at the office.
For more meanings of the phrasal verb show off, follow the link.
more information: show off
Here thought is the past tense of the irregular verb think. Follow the link to listen to some examples.
more information: think
in that
Follow the link to find out when to spell the word principle or principal.
more information: principal & principle
die out
become uncommon and then disappear
Example: The corner shop is slowly dying out.
old timers
old people; people who have been doing something for a long time
Example: One way to revitalise the company would be to get rid of all the old timers.