Sinuous: undulating; curved in and out.
Sinus: a curvilinear indentation more or less profound: an excavation as if scooped out: a curved break in an otherwise straight margin.
Siphon: a tube-like mouth organ in certain insects: the breathing tube of a Culicid larva: any tubular external process or structure.
Siphonaptera: an ordinal name for insects which are wingless: mouth formed for piercing and sucking; saltatorial; transformations complete: the fleas = Aphaniptera; q.v.
Siphonata: = Homoptera or, more specifically, plant lice and leaf hoppers.
Siphonets: see honey tubes.
Siphonophora: = Coccinellidae; the term is preoccupied in the Coelenterates.
Siphunculata: the sucking lice.
Siphunculus: the suctorial organ of a louse, contained within the tubule: in plant lice =honey tubes; q.v.
Situ (in): in its natural place or position.