also: いささ
prefix
Archaic prefix meaning 'small' or 'little'. The reading いさら is especially associated with water (e.g., いさら川 for a small stream). The alternate reading いささ is less common. This prefix is not productive in modern Japanese and appears only in a few fixed expressions.
古い歌に「いさら川」という言葉が出てくる。
The word 'isaragawa' (small stream) appears in old poems.
「いささか」の語源は、この「いささ」に由来するとも言われる。
It is said that the etymology of 'isasaka' (a little) comes from this 'isasa'.
Kanji spelling for いさら; rarely used in modern Japanese.
いささか is a modern adverb meaning 'a little' or 'somewhat', possibly derived from the archaic prefix いささ. Unlike いさら/いささ, いささか is still in common use.
The exact derivation is uncertain. It is an archaic prefix meaning 'small', with the いさら variant often associated with water. The form いささ may be related to the modern adverb いささか.