pre-noun adjectival
(not) any particular; (no) special; (not) noticeable
Pre-noun adjectival used only in negative contexts. It emphasizes that nothing stands out or is worth mentioning. Common patterns: さしたる～もない, さしたる～はない.
さしたる理由もなく欠席した。
I was absent without any particular reason.
彼の話にはさしたる興味が持てなかった。
I couldn't take any particular interest in his story.
大した is used in both positive and negative contexts to mean 'great' or 'considerable', while さしたる is only used negatively to mean 'no particular'.
特に is an adverb meaning 'particularly' or 'especially', and can be used in affirmative sentences, unlike さしたる which is restricted to negative contexts.
Derived from the classical verb 然す (さす, 'to be so') in its attributive form 然したる, which became a fixed pre-noun adjectival. The exact historical development is uncertain, but it has been used in negative constructions since at least the Edo period.