adverb
without delay; smoothly; without a hitch
Describes an event or process proceeding without obstacles, delays, or problems. Often used in formal or business contexts.
See also: 滞り
会議は滞りなく終了した。
The meeting concluded without a hitch.
手続きが滞りなく進むように準備しておきます。
I will prepare so that the procedures go smoothly.
滞る is the verb meaning 'to be delayed' or 'to be held up'; 滞りなく is the adverbial form meaning 'without delay'.
スムーズに is a common loanword meaning 'smoothly', but 滞りなく carries a nuance of 'without any hindrance or delay' and is slightly more formal.
Derived from the verb 滞る (とどこおる, 'to be delayed') with the adverbial suffix なく, meaning 'without'.