Godan verb with 'mu' ending, Transitive verb
to insert
「ええ、そうね」とスーザンが言葉をさしはさむ。「私が電話したのは・・・」"Ah, that's true," Susan puts in, "I just wanted to call to ..." to interrupt; to slip in a word
to harbor (e.g. doubts); to harbour; to entertain (e.g. a theory)
Also written 挟む【さしはさむ】、差し挾む【さしはさむ】