厳しい

Etymology 1
Originally from regular classical adjective, first cited to roughly 830.

This earlier form later shifted conjugation patterns, from the so-called "-ku adjective" to the "-shiku adjective" pattern. The two conjugation types appear to have been in broadly free variation, with both forms developing the senses in parallel. Historically, while there was some overlap, there does appear to be a sense distinction in Classical Japanese texts, wherein the older "-ku adjective" form was used more commonly to express the more objective qualities of "tight, close", while the "-shiku adjective" was used more commonly to express the more subjective qualities of "severe; harsh".

The "-shiku adjective" pattern is first cited from the late 900s.

Adjective

 * 1)  stern, grave, forbidding; dignified, stately
 * 2)  strict, unforgiving
 * 3)  tight, close, without gaps
 * 4)  harsh, tough, extreme, severe, hard to withstand
 * 5)  extreme, excessive, terrible
 * 6)  dire, difficult, tight
 * 1)  dire, difficult, tight
 * 1)  dire, difficult, tight

Adjective

 * 1)   wondrous, miraculous, splendid, sublime
 * 2)   dignified, solemn, stern, noble, refined
 * 3)   beautiful, pretty
 * 4) * c. 14-16th century: Kazashi no Himegimi
 * 姫君一人おはします. [...] 御かたちを見るに、髪のかかり、眉、口つき、いつくしくて [...]