To insert anything somewhere (especially between other things), such as an affix into a word. (Compare interpolate.)
To insert an extra month into a calendar for the same purpose. The Hebrew calendar has such a month.
To insert a substance between two or more molecules, bases, cells, or tissues.
To insert an extra leap day into a calendar in order to maintain synchrony with natural phenomena.
To insert something (or oneself) between other things.
To interrupt a conversation by introducing a different subject or making a comment.
To intervene in a dispute, or in a conversation.
To be inserted between parts or things; to come between.
To offer (one's help or services).