always used before a noun
chiefly US
1
: used or chosen first
first-line treatment/therapy
2
: available to be used immediately
first-line troops
Cite this Entry
“First-line.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/first-line. Accessed 16 Apr. 2026.
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