Very formal but not Blimpish (5)

I believe the answer is:

rigid

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

'very formal' is the definition.
'rigid' can be an answer for 'formal' (thesaurus). I am unsure of the 'very' bit.

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for rigid that I've seen before include "Stiff and inflexible" , "Stiff, unmoving" , "completely" , "Incapable of or resistant to bending" , "stern" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app