particularly; especially; in particular
Used with a negative predicate to mean 'not particularly' or 'nothing special'. The negative is usually explicit, but can be implied in informal speech.
I don't have anything in particular to do today.
This movie isn't particularly interesting.
From the verb 取り立てる (to collect, to pick out) in its te-form, used adverbially. The negative usage developed from the idea of 'not singling out' something.