Crossword Genius

Express heading for Swansea at the busiest time (5)

Ross

I believe the answer is:

speak

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

'express' is the definition.
(I've seen this before)

'heading for swansea at the busiest time' is the wordplay.
I cannot quite see how this works, but
'busiest' could be 'peak' (I've seen this in another clue) and 'peak' is found in the answer.
A single letter 's' remains which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for speak that I've seen before include "Talk" , "Utter words" , "Converse" , "Say something" , "express" .)

I've seen this clue in The Independent.
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