Man pages matching name qwtclipper in section 3:

QwtClipper.3.en	debian 10 / libqwt-doc
QwtClipper.3.en	debian 10 / libqwt5-doc
QwtClipper.3.en	debian 11 / libqwt-doc
QwtClipper.3.en	debian 12 / libqwt-doc