What is the meaning of Sely?

Obsolete form of silly, especially in its older senses like "innocent", "pitiable, poor", "trifling, insignificant", but also "foolish".

inflection of sít:

  1. inanimate masculine plural past active participle
  2. feminine plural past active participle

inanimate masculine plural past active participle

feminine plural past active participle

instrumental plural of selo

Source: wiktionary.org