groundless
He accuses them, not quite groundlessly, of being inconsistent.
He complained endlessly and groundlessly about unfair treatment.
They groundlessly assume that these decisions are influenced by socioeconomic forces.
We may feel (however groundlessly) that a child's character traits are directly linked to those of the parents.
They were groundlessly linked to the case.
Perhaps groundlessly, they are convinced that the train will not arrive.

SMART Vocabulary: related words and phrases

Too much and unnecessary
ado
be up to your neck (in something)idiom
bellyful
binge
carry/take coals to Newcastleidiom
drown
gush
hyper
immoderate
immoderately
inappeasable
inessential
infest
plenty
pleonasm
pleonastic
plethora
proliferation
unwarranted
weigh someone/something down