From Wiktionary, the free dictionary
From surreptitious + -ly .
surreptitiously (comparative more surreptitiously , superlative most surreptitiously )
In a surreptitious manner; stealthily , furtively , secretly .
Synonyms: furtively , secretly , stealthily
1909 , Archibald Marshall [pseudonym; Arthur Hammond Marshall], “A Court Ball”, in The Squire’s Daughter , New York, N.Y.: Dodd, Mead and Company , published 1919 , →OCLC , page 9 :They stayed together during three dances, went out on to the terrace, explored wherever they were permitted to explore, paid two visits to the buffet, and enjoyed themselves much in the same way as if they had been school-children surreptitiously breaking loose from an assembly of grown-ups.
in a surreptitious manner
Azerbaijani: gizli (az)
Bulgarian: скришом (bg) ( skrišom ) , крадешком (bg) ( kradeškom )
Catalan: subreptíciament (ca) , d'amagat (ca) , d'amagatotis (ca) , celadament (ca) , furtivament (ca) , amagadament (ca)
Czech: tajně (cs) , skrytě , potají (cs)
Danish: hemmeligt
Dutch: clandestien (nl) , heimelijk (nl)
Finnish: vaivihkaa (fi) , salaa (fi)
French: subrepticement (fr) , furtivement (fr)
German: heimlich (de)
Irish: gan fhios
Italian: furtivamente (it) , di nascosto
Kurdish:
Northern Kurdish: bi dizîkî , bi nehînî , bi razberî
Norwegian:
Bokmål: i smug , i skjul , i løyndom
Persian: محرمانه (fa) ( mahramāne )
Portuguese: sub-repticiamente (pt) , furtivamente (pt) , disfarçadamente
Romanian: pe ascuns , pe furiș
Russian: тайко́м (ru) ( tajkóm )
Serbo-Croatian: potajice (sh)
Somali: sir
Spanish: subrepticiamente (es) , a hurtadillas , callando (es) , callandito
Swedish: i smyg (sv)
Turkish: gizli (tr) , gizlice (tr) , el altından (tr)