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Definitions

key

[kee] / ki /
ADJECTIVE
essential, important
Synonyms
STRONGEST
basic crucial decisive fundamental indispensable leading main major pivotal primary principal vital
STRONG
chief material
Antonyms
STRONGEST
additional auxiliary extra inessential insignificant lesser minor nonessential secondary subordinate trivial unimportant unnecessary
NOUN
item that unlocks
Synonyms
STRONG
latchkey opener passkey screw skeleton
Antonyms
WEAK
lock question
NOUN
answer, solution
Synonyms
STRONGEST
blueprint clue code core guide indicator means passport password sign ticket
STRONG
brand cipher crux cue earmark explanation fulcrum hinge index interpretation lead lever marker nexus nucleus pivot pointer root symptom translation
Antonyms
STRONG
exterior exteriority outside
WEAK
lock question

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

Touted for years by Musk as the key to taking humans to Mars, SpaceX is now looking to show that Starship can work, including by lofting the company’s own satellites into orbit.

From The Wall Street Journal • Apr. 4, 2026

Low metallicity is a key indicator of age.

From Science Daily • Apr. 4, 2026

Grimes added citizen scientists in Plymouth and surrounding areas "can help overcome a key challenge in urban micrometeorite research, accessing multiple sample sites and processing material to build a national archive".

From BBC • Apr. 4, 2026

EssilorLuxottica carries none of that baggage while being Meta’s key partner in smartglasses.

From The Wall Street Journal • Apr. 4, 2026

Auntie North fished in her blazer pocket and withdrew an old-fashioned brass key.

From "The Way to Rio Luna" by Zoraida Cordova

From Roget's 21st Century Thesaurus, Third Edition Copyright © 2013 by the Philip Lief Group.