The spelling with a u instead of a v, favoured by some editions, suggests a link with scieu, the past participle form of saver1, which, used adjectivally (‘known’) may also have produced an adverb *scieument.
adv.
1knowingly, in full knowledge:
(
1360
)
leurs diz ennemiz passer ne demorer scieument (l. scienment) souffrerons
iii 530
(
1362
)
Et si nous faceons, procureons, ou suffrerons sciennement le contraire estre fait [...]
iii 663
(
1367
)
Ne yceulx ennemis, au domage ou prejudice de nostre dit frere, ses heirs, ou le roialme de France, scienment receptrons [...] en nostre roialme
iii 835
scienment (1360)