See eg red and white Sierra carrying tonnes (7)
I believe the answer is:
witness
'see' is the definition.
('witness' can be a synonym of 'see')
'eg red and white sierra carrying tonnes' is the wordplay.
I cannot quite understand how this works, but
'and' could be 'n' (common abbreviation for 'and') and 'n' is found in the answer.
'white' could be 'w' and 'w' is found within the answer.
'sierra' could be 's' (phonetic alphabet: alpha, bravo, charlie etc.) and 's' is located in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for witness that I've seen before include "Observe - evidence" , "Court testifier" , "Evidence, proof" , "It's news (anag.)" , "Observer" .)