i Register
In some senses, sincere is marked as archaic. Watch for register when choosing this word.
VERBS
be, look, seem, sound
ADV
deeply, really, very
She was really sincere when she apologized to her friend for missing the birthday party.
completely, entirely, perfectly, quite, utterly, wholly
enough
His apology was sincere enough, though she still needed more time to trust him again.
PREP
about
She was never sincere about why she decided to quit her job.
in
We were not sincere in our apology because we didn't really mean what we said.