Sentence:  The shampoo bottle closures included a screw cap closure considered to be the most vulnerable during use, a flip or <WSD>snap cap</WSD> with a circular orifice considered to offer the greatest degree of protection, and a flip cap with a slit orifice whose protective abilities were unknown at the time. 
Meaning of the word marked with <WSD> tags:  A (cap) or cover that snaps into place.