Definition of baseline
1 : a line serving as a basis especially : one of known measure or position used (as in surveying or navigation) to calculate or locate something
2a : either of the lines on a baseball field that lead from home plate to first base and third base and are extended into the outfield as foul lines
b : basepath
3 : a boundary line at either end of a court (as in tennis or basketball)
4 : a usually initial set of critical observations or data used for comparison or a control
5 : a starting point
the baseline of this discussion
Keep scrolling for more
Keep scrolling for more
Keep scrolling for more
Keep scrolling for more
Test Your Vocabulary
Slippery Words Quiz—Changing with the Times
- What is an earlier meaning of nice?

Test your knowledge - and maybe learn something along the way.
TAKE THE QUIZ
A daily challenge for crossword fanatics.
TAKE THE QUIZLove words? Need even more definitions?
Merriam-Webster unabridgedWords at Play
Ask the Editors
Word Games
Slippery Words Quiz—Changing with the Times
Do you know these earlier meanings of words?
Take the quizWords of Snow and Ice Quiz
A selection of words from the chillier parts of t...
Take the quizTrue or False?
Test your knowledge - and maybe learn something a...
Take the quizWord Winder's CrossWinder Play the game
Share baseline
Time Traveler for baseline
The first known use of baseline was circa 1556
See more words from the same year