barely audible, the barest, faint, gentle, hushed, low, mere, quiet, slight (esp. AmE), soft
A barely audible whisper came from the closet.
Jake got excited at the merest whisper of his lover.

fierce, harsh
audible, loud, stage
‘I knew this would happen,’ he said in a stage whisper (= one that he wanted everyone to hear).

choked (esp. AmE), hoarse, husky
excited, urgent
conspiratorial

hear

above a whisper
Their voices were very quiet, hardly above a whisper.

in a whisper
They spoke in whispers.

gently, quietly, softly
loudly
hoarsely, huskily
fiercely, harshly, urgently
‘Come on,’ he whispered urgently.

brokenly, shakily
angrily, bitterly, furiously
conspiratorially
excitedly
almost, half
barely (esp. AmE)
back
‘Yes,’ I whispered back.

can only
He could only whisper in reply.

hear sb
She heard him whisper her name.

about
I felt that everyone was whispering about me.

against
‘Hush!’ he whispered against her hair.

through
‘No!’ he whispered through gritted teeth.

to
‘Let's go,’ she whispered to Anne.

whisper sth in sb's ear, whisper sth into sb's ear

Whisper is used with these nouns as the subject:
voice

Whisper is used with these nouns as the object:
apology, prayer, word