Learners’ Dictionary

1.ultrasonic
major definitions:
ultrasonic sound waves are too high for humans to hear
example sentence:
Cats, too, are sensitive to ultrasonic frequencies and can hear mice and voles in hidden places.
2.scanner
major definitions:
a machine that passes an electrical beam over something in order to produce a picture of what is inside it
example sentence:
The developer hopes it would link with the existing Magnetic Imaging Centre, which already operates a sophisticated body scanner.

3.drum up
major definitions:

examto get support, interest, attention etc from people by making an effortple sentence:
example sentence:
The drums then took up a regular beat as he stalked back to the coffin.
4.compelling
major definitions:
very interesting or exciting, so that you have to pay attention
example sentence:
This approach to the nature of dreaming is highly compelling.

5.challenging
major definitions:
difficult in an interesting or enjoyable way
example sentence:
This has to be achieved without adversely affecting design quality, a task that can prove quite challenging.