in line is an adjective and adverb meaning "being next in a line of succession". It carries 3 recorded senses.
awaiting something; especially something due
“people were in line at the checkout counter”
“she was in line for promotion”
one behind another in a line or queue
“they waited in line for the tickets”
Definitions, synonyms and semantic relations for in line come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.