Come across as they arrive? (6)
I believe the answer is:
appear
'arrive?' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for appear that I've seen before include "Develop" , "Surface" , "be published" , "Show up, become visible" , "Look - materialise" .)