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Definitions

on the sly

ADJECTIVE
subterrestrial
Synonyms
WEAK
alternative avant-garde clandestine concealed covert experimental hidden hush-hush hypogeal hypogean hypogeous on the Q.T. private radical resistant resistive revolutionary subterranean surreptitious unbowed unconventional under wraps undercover unusual
ADJECTIVE
surreptitious
Synonyms
STRONGEST
clandestine covert furtive hush-hush unauthorized
WEAK
fraudulent hidden hole-and-corner on the Q.T. private skulking slinking sly sneaking stealthy sub-rosa under wraps under-the-table undercover underhand veiled
Antonyms
STRONGEST
aboveboard forthright honest open public truthful
WEAK
authorized
ADJECTIVE
underground
Synonyms
STRONGEST
clandestine experimental hidden private
STRONG
alternative avant-garde covert radical revolutionary
WEAK
concealed hush-hush on the Q.T. resistant resistive surreptitious unbowed unconventional under wraps undercover unusual
Antonyms
STRONGEST
open
STRONG
conservative
WEAK
aboveground authorized condoned ground known legal public sky
ADVERB
covertly
Synonyms
STRONGEST
clandestinely secretly surreptitiously
WEAK
by stealth furtively hush-hush in camera in holes and corners on the Q.T. on the quiet privately slyly stealthily sub-rosa under wraps undercover wildcat
Antonyms
WEAK
candidly frankly honestly openly overtly publicly
ADVERB
secretly
Synonyms
STRONGEST
clandestinely covertly furtively personally privately quietly stealthily surreptitiously
WEAK
behind closed doors behind someone's back by stealth confidentially hush-hush in camera in confidence in holes and corners in secret in strict confidence insidiously intimately obscurely on the Q.T. on the quiet privily slyly sub-rosa under the table underhandedly unobserved
Antonyms
STRONGEST
publicly
WEAK
openly

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.

The math-proficiency analysis suggests it may be doing so on the sly.

From The Wall Street Journal • Nov. 30, 2025

Some people were there to raise money on the sly, and given the big money behind WelcomeFest, it wasn’t a bad idea.

From Slate • Jun. 9, 2025

When Burnett was growing up in Brooklyn, dancing was something he had to do on the sly.

From New York Times • Jul. 23, 2021

A vivid and wryly-observed pop anthem, it sees Peters confronting an ex who badmouths her in public, but still calls her on the sly.

From BBC • Jun. 15, 2021

If we had one, I could befriend an actor or two, and get them to keep training me on the sly.

From "You Bring the Distant Near" by Mitali Perkins

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