Transport essential to divers (7)

I believe the answer is:

airline

I'm a little stuck... Click here to teach me more about this clue!

'transport' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I don't see?

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for airline that I've seen before include "company supplying transport" , "Business taking off" , "It creates inflation" , "Aircraft operating company" , "SAS perhaps" .)

I've seen this clue in The Globe and Mail.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.