Burning gas able to move easily (5)

I believe the answer is:

lithe

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

'able to move easily' is the definition.
I can't tell whether this definition defines the answer.

'burning gas' is the wordplay.
'burning' becomes 'lit' (I've seen this before).
'gas' becomes 'he' (chemical symbol for helium).
'lit'+'he'='LITHE'

Can you help me to learn more?

(Other definitions for lithe that I've seen before include "Don -, opera by Verdi" , "able to move supply" , "Elastic" , "showing great athletic ability" , "Supple and graceful" .)

I've seen this clue in The Guardian.

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.