“F1”

We have one entry that includes the term F1.

F1 layer

noun

: the lower of the two layers into which the F region of the ionosphere splits in the daytime that occurs at varying heights from about 80 to 120 miles (130 to 200 kilometers) above the earth's surface

See the full definition

Word of the Day

Listen to the pronunciation of complaisant

See Definitions and Examples »

Test Your Vocabulary

Challenging Standardized Test Words, Vol. 2

  • a pencil broken in half on top of a test answer sheet
  • The business’s new computer system proved not to be a panacea.
How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

TAKE THE QUIZ
Play Blossom: Solve today's spelling word game by finding as many words as you can using just 7 letters. Longer words score more points.

Pick the best words!

PLAY
Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Games & Quizzes

See All
Play Quordle: Guess all four words in a limited number of tries. Each of your guesses must be a real 5-letter word.
Quordle Can you solve 4 words at once?
Play Blossom: Solve today's spelling word game by finding as many words as you can using just 7 letters. Longer words score more points.
Blossom Word Game Pick the best words!
Play Missing Letter: a crossword with a twist. Each of the 25 puzzle words start with a different letter of the alphabet. Which letter is missing?
Missing Letter A daily crossword with a twist
sweet smart pug puppy dog sitting in front of blackboard with chalk question marks
Commonly Confused Words Quiz Vol. 3 Do you have a (flare/flair) for choosing the righ...