Dated synonym for 簡単; used in older texts or formal contexts. In modern Japanese, 簡単 is the natural choice.
See also: 簡単
This problem can be solved simply.
His explanation was simple and easy to understand.
Dated kanji spelling; 簡単 is the modern standard.
Variant kanji spelling, also dated; 簡単 is preferred.
A kanji compound of 単 (simple) and 簡 (simplicity), forming a word that is essentially synonymous with 簡単. The exact historical derivation is uncertain, but it is now considered dated.