How to Say "long line" in Spanish
The Spanish word for “long line” is “procesión” — B2 level.
English → SpanishB2
nounB2
a sequence of objects or people

Examples
Había una procesión de hormigas en la cocina.
There was a long line of ants in the kitchen.
Una procesión de coches bloqueaba la carretera.
A long line of cars was blocking the highway.
Figurative Usage
You can use this word to emphasize that a line of things is very long and moving slowly, just like a religious march.
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